What the?!?
So, you just got your brand new program. AND BAM, you cant use it because you dont have .NET 4.0
Well your in the right place.
The picture above is shows what download you will need.
If you have a 32 bit computer you want the RED download
If you have a 64 bit computer you want the BLUE download
If you have a i86 or i64 bit computer you will want the GREEN download.
If you are unshure what "bit" you are download the RED.