Re: OS 32bit or 64bit
Certain intensive calculations such as video encoding, work somewhat faster on 64-bit. You can also natively handle 4GiB of RAM or more on 64-bit.
Of course, 64-bit operating systems only work on 64-bit CPUs. Look up your CPU on Wikipedia and it will say if it is 64-bit or not. Most in the last six years are.
You would have to reinstall Ubuntu to get 64-bit; not worth it in my opinion, just install 64-bit the next time you do a clean install of Ubuntu.
I hope my advice helps. Please let me know whether it did!