Yes, but how much it's going to cost you depends on your setup.
If you purchased a prebuilt computer (Dell, HP, eMachines, etc.) with an OEM license of Windows Vista, then you'll have to purchase a new license along with a 64bit disc. If that is the case, I recommend you get Windows 7. An upgrade disc will do, they run about $100.
If you have a retail version of Windows Vista (that includes the upgrade version), then you can go to this website:
http://www.microsoft.com/windowsvista/1033/ordermedia/default.mspx
and Microsoft will send you a 64bit version of Vista for a small fee (~$10).
In any case, you will have to perform a clean install to make the move from 32bit to 64bit.