Windows 7 home premium is available in 32/64 bit versions.
What matters is, whether your computer supports 64bit or not?
Quoted from the above link
What is the difference between 32-bit and 64-bit versions of Windows?
The terms 32-bit and 64-bit refer to the way a computer's processor (also called a CPU), handles information.
The 64-bit version of Windows handles large amounts of random access memory (RAM) more effectively than a 32-bit system.
Every version of Windows 7 comes in two forms, with 32 bit and 64 bit . Normally if you buys something these days, any system having a dual core process Intel or AMD will support 64 bit OS.
Only some Applications are still not compatible with 64 bit which inludes loads of drivers for your hardware expecially old ones.
For the new ones, you can safely go for 64 Bit as they will be supporting RAM more than 4 GB whereas 32 bit supports only upto 4 GB.