Going from 32-bit Windows 7 to 64-bit Windows 7 means installing a whole new operating system. Despite that they are "both Windows 7" they have less in common "under the hood" than different 64-bit versions of Windows. So you'd be doing a "Custom install" which means the installer would back up certain files, do a clean install of the 64-bit operating system, and then copy back the files it backed up (to the best of its ability).
It's up to you if you want Windows 7 or Windows 10.
I suggest you look at a Windows 10 computer in a store or at a friend's house to see if you are OK with the changes in the interface.
You have to decide for yourself if you can live with Windows 10, or if you'd rather have Windows 7.
Another thing to consider is that 64-bit Windows 7 will probably be more "compatible" with certain older games than 64-bit Windows 10. Check the Windows 7 and Games thread as opposed to the Windows 10 and Games thread. This isn't limited to "games from the 1990's" and can apply to much newer games.
Windows 7 will be supported with security updates until 2020 according tohttps://support.microsoft.com/en-us/help/13853/windows-lifecycle-fact-sheet
So there's no hurry to get Windows 10, and you may want to wait until you get a new computer or upgrade your current one with hardware that requires Windows 10 before switching to Windows 10.