Ram sticks are neither 32 bit or 64 bit. The only contain different amount of ram. IE like a 1 gig stick, 2 gig stick,4 gig etc.

Upgrading the amount of ram is just a matter of replacing the current sticks with larger size ones. Normally there are 4 ram stick slots on a mother board and ram should always be installed in pairs to achieve the best performance. So for example if you want 4 gig of ram in your system you can either put 4 1 gigs sticks using all four slots or 2 2gig sticks using 2 slots. 

Ram should all be the same speed ie like 400 mhz 800mhz 1066mhz. The higher the speed rating the more costly the ram will be. 

800mhz ram is at the moment generally the best bang for the buck. For running everyday applications it is more than sufficient.