Which software specifically are you trying to run, most 32bit software will automatically work fine on a 64bit OS.
If it does not then good chance you will need to run it in a virtual machine or download a 64bit version.
As for changing to 32bit windows from 64bit, you would have to wipe your system and reinstall windows (32bit). This would limit you to 3gb ram maximum, even if you have more it will not be used. So I wouldn't recommend it these days.