CentOS is most popular operating system on Linux servers. If you want to check the CentOS version installed on your server, please refer to our following tutorial page:
How to find CentOS version installed
If you want to check centOs installed on your server is 32-bit or 64-bit, here is how you can find.
Login in your server via SSH as root and execute following command.
If the output shows i686 or i386, this means its a CentOS 32-bit.
And if the output shows x86_64, this means its a CentOs 64-bit.