if you really should increase some storage i would choose a bigger SSD.
The 64gb SSD is gonna have 60 GB in the standard human number system. (In the standard human number system 1000MB is equal to 1 GB, but the computer counts it as 1024MB is equal to 1GB)
Then windows 7 takes ruffly 25 GB. So you are left with only 35 GB for other stuff.