how many bits is my computer 32 or 64

There are two things to check:

1. If the CPU is a 64 bit CPU:
Open the Terminal and run
cat /proc/cpuinfo
This will return a lot of information, repeated for every CPU/core. It the CPUs have the flag "lm" they are 64 bit.

2. If the OS is 64 bit:
Run
uname -m
If the result is "x86_64" it is 64 bits.

A 32 bit OS can run on a 64 bit machine, but not the other way around. 64 bit software needs both OS and CPU to be 64 bit.

If you are still lost, if you can give a system make and model then you can use the web to find out using manufacturers website