Yes to uninstalling Start8 before installing Start10.  Start10 should be installed after installing Windows 10 as the installer would block installation on Windows 8.

Followup clarification question about Banfield's post.  It's understood that Start10 can't be installed under Windows 8.1.  However, if a Start8 user wants to preserve their Start8 settings, is it possible to follow the sequence of first installing the MS Windows 10 upgrade, and then running the Start10 installer, which (1) picks up previous Start8 settings, (2) uninstalls the old Start8, and then (3) installs the new Start10 with the previous configuration settings preserved?   

fyi U can use start8 on Windows 10 just fine

FYI you can INSTALL Start10 ON windows 8.1 how ever it will refuse to load.. Dose not mean you can not install it..

SO if I was me.. which I em me, and I have both start8 and 10 for the sake of headache free upgrade Ill be uninstall Start8, as well as Any video drivers, and device that may have a issues during the upgrade followed by past experiences

but yes you could install Start10 on Win8.1 prior to upgrading.. and yes it will work after upgrade, I done this a few time already with each new Build MS drops.

Question for The_Gear, or anyone else wgo may have an answer for me:

I am really confused right now, and the Windows 10 update is only a day or so away. I currently have Start8 1.5 installed on two desktops running Windows 8.1, and both will be upgraded to Windows10. I have already downloaded the new Start10 file, in order to eventually install on the PCs with the new Windows10 OS in place. Whenever I tried uninstalling Start8 using the native Windows "program uninstall" feature, I was warned that because Start8 was still running, I would be unable to proceed. I am not sure if finding and "stopping the service' would be enough to allow me to proceed. And, I can find no "uninstall" provision on the Start8 Menu box, (or anywhere else, for that matter) only a button to "deactivate license". Now, if I were to select "Deactivate license", would I THEN be prompted to uninstall Start8 in a sure & proper manner, so that I could cleanly install the newer Start10 AFTER I have upgraded these PCs to Windows10?? Thank you in advance, I really don't want to mess anything up here!

Thanks for your kind reply, The_Gear.

Just so I don't mess things up too badly during my Windows10 update tomorrow, I was wondering if I could just LEAVE Start8 installed on the machine I was updating, and then AFTERWARDS, install Start10. I had seen some other posts that said that Start8 works "just fine" on Win10, at least initially. And since uninstalling Start8 by executing the procedure you recommended above might possibly NOT uninstall everything correctly the first (or even second) time around, I am fearful of the mess I might wind up with afterwards. Does installing Start10 OVERWRITE (or otherwise REMOVE) the currently resident Start8 program?? Or will Start8 STILL have to be uninstalled before installing Start10?? If there is no real problem with just LEAVING Start8 alone during my Win10 upgrade, and then installing Start10 after the dust has settled, might THAT be the way for me to go here? I was planning on uninstalling Fences and IconPackager (the only other two Stardock programs that are presently installed) prior to the Win10 upgrade to lessen any potential conflicts..or should I? Sorry about so many questions here, but I've been burned so many times over the years with program incompatibilities during OS upgrades, I guess that I'm really gun-shy here now. Thank you a TON for your advice here, The_Gear!!!

Thanks for the reply, Gear! I will let you know if I have any problems then. You didn't mention, but if all goes well after the Win10 install, would my installing Start10 afterwards OVERWRITE/REPLACE the older Start8 software? Or would I physically have to attempt the Start8 uninstallation before proceeding with the Start10 installation? Sorry for so many nagging questions, but I'd really like to be sure! I do appreciate your advice in all of this! THANKS AGAIN!

Thank you for all your timely advice, Gear!

Very helpful. I had uninstalled Start8 before upgrading to Win10, just in case, because it was problematic on a Gateway all-in-one earlier, not easy to uninstall afterwards. I have not yet tried installing Start10 on my HP, because I'm happy enough with the new Start supplied by Win10. Fences appears to work just fine under Win10, so that's all I'll be using (at least for a while) until everything settles down a bit.