It is possible to switch to 64 bit yes but you have to first make sure you have the hardware needed to run a 64 bit OS.. Like a 64 bit compatible CPU for example..
If you do then all you have to do to switch is a clean install of Windows 7 64 bit edition.. unfortunately you can't just do an upgrade from an x86 OS to an x64 OS.. it has to be a clean install (as in format the partition you wish to install on then install win 7 64 bit).. As far as it being worth it or not.. well that all depends on what you use your pc for.. if all you do is surf the web, read emails, watch videos.. then no it's not really worth the switch.. However, if you do heavy video editing or heavy gaming for example than yes the switch would be worth it in my opinion...
Also, drivers for a 64bit OS CAN be more difficult to find than drivers for 32 bit OS's.. though that's becoming less of an issue these days as more and more people are switching to 64 bit OS's as their primary OS.. I'd suggest doing some research first on your hardware and making sure there are 64bit drivers available for each component first...
That all being said, I should also point out the RAM issue... the biggest advantage to using a 64 bit OS is the fact that it let's you make full use of 4GB's of RAM.. OR MORE (128GB + ) So if your system has 4GB, 6GB, 8GB, 10GB of RAM ... (you get the picture) than 64 bit is an excellent choice because you'll actually get to see/use all of it..
If you only have 2GB's installed though then 64bit wouldn't really be worth switching to in my opinion..
Hopefully that clears it up a bit for ya..