You need W10 64-bit as said above.
You will also want to plan very carefully to avoid losing data. I suggest you buy a new HDD or SSD (such as 250GB Samsung SSD) so you can keep the original untouched to boot back into in case you forgot some files or info.
*there are ways to avoid re-downloading the games such as:
a) reinstall Steam to W10, then
b) create a new folder in Steam library settings (i.e. "E:\Steam"), then
c) create that folder on the E-drive (HDD with Steam games) and cut/paste the entire "Steamapps" folder over
Some SAVES are cloud-based so fine and others will be somewhere in the "Documents" or "Documents->My Games" sub directories... so keep the entire Documents folder saved for that and other data.
So basically:
0) have the W10 login e-mail + password ready for install (i.e. MSN account)
1) obtain a W10 64-bit install media
2) shut down and UNHOOK all drives
3) hook up the new drive
4) install (will need password)… there is AUDIO now too so have speakers hooked up but not necessary
5) let MS Updates finish (start->settings->update&security)
6) install programs, drivers (if in doubt do NOT install a driver), setup fan software/profile as needed
7) transfer games
8) when satisfied, DELETE what you don't need for old Windows on other HDD/SSD, then make a BACKUP IMAGE of the Windows drive to secondary storage...Acronis True Image or similar.
*This is most, but not all, of what you want to do. Again, plan carefully and if possible avoid using the original Windows drive at all.