You don't have to wait. Microsoft provides a tool to manually download the upgrade at
https://www.microsoft.com/en-us/software-download/windows10When you run it, you can opt to do an in-place upgrade or create a DVD or USB installer kit. If you select the latter, you can later do a clean install if you want.
Be sure to do a full backup of your computer before doing the upgrade, just in case.
Unfortunately, Windows 10 defaults to being spyware. Make sure you go through the Privacy settings and turn off all of the options. If you value your privacy, you also shouldn't use either Cortana or Edge. There are a lot of apologists who say it's no big deal because just about all the tablet and phone vendors are doing it, but I think that's being irresponsible.
In most cases the upgrade procedure can upgrade a fully patched Win7 SP1 or 8.1 with no problems at all, although it does download over 1GB of patches in addition to the base upgrade files.
On my computer it invalidated the previous disk search cache and had to rebuild it from scratch. While that's running, all disk accesses are *very* slow. If you have many files, it could take several hours to re-index everything, as it did on mine. Of course, if you do a clean install, there's not much to index, so you probably wouldn't notice that happening.
A clean install, wiping out all your files, can only be done after you've done an upgrade and the activation procedure has successfully registered your computer with Microsoft's servers. Otherwise you need a Windows 10 product key: your old Win7 or Win8 key is not valid for Win10.
Nvidia's GeForce Win10 graphics driver still has some issues, which might be the cause of some problems and slowdowns. Its discussion forum is 81 pages already, so you might want to skip to the end.
See
https://forums.geforce.com/default/topic/860152/official-windows-10-353-62-game-ready-display-driver-feedback-thread-7-29-15-/Some Firefox weirdnesses can be cleared up by disabling Firefox's hardware acceleration, which is enabled by default.
