There is NO upgrade from 32 to 64 bit. Let's grind on this for a moment. While one can upgrade the license the install of the 64 bit does not offer an in place upgrade from 32 to 64 bit.
This is well discussed in the Windows 7 forum.
I strongly suggest you move to the 64 bit version and stay there.
I?m planning to buy Dell Vostro 3500 laptop (T520722IN8) with i5 processor and 4 GB RAM. It is available in different OS options. I would like to know if I buy this laptop with Win7 Home Basic 32bit OS, will I be able to install Win7 Home/professional/Enterprise 64 bit OS later on? Will I need to update any hardware drives for that?