Upgrading to 64 bit comes into play if you want to build complex models otherwise with 2GB of RAM you can get an out of memory error when rendering.
But, if you do, make sure Windows knows about it as when I do a periodic reinstall of Win7 it reverts to the factory setting of 2GB on my 7GB machine and only 1 core. To cure that and to speed up the boot, left click Start and type msconfig into the search. Click on the boot tab and then Advanced Options. Click the Number of Processors radio button and select 2 from the pull down. Also click the Maximum Memory box to see above the original setting. Click OK to go out and reboot.
Can you still get Win7? To me Win8 is just Win7 with a touchscreen overlay but with the new Start screen just an irritation.
I can recommend googling Crucial and use their advice thingy to check your machine and recommend additional memory at a reasonable price.