1) As said you can't, but could you explain WHY you'd want to? Perhaps there's another issue you need solved instead?
The ONLY advantage 32-bit offers is support for certain devices which never got driver updates to 64-bit. On the other hand, having 32-bit for the OS severely limits the amount of memory (Video and System) that can be addressed.
2) Just FYI, but the term "x86" doesn't technically mean "32-bit" but most people including Microsoft use the incorrectly. The term "x86" refers to the instruction set for which 32-bit and 64-bit CPU's exist.
It should be:
x86_32, or
x86_64