How do I change my computer from 32 bit to a 64 bit?

You don't, because there is no need to unless you Mac is about 14 years old. All Macs made since 2007 at the latest have 64-bit processors. It is software that needs to change and only the software developer can fix that.

Pleas see this Apple Support article to learn how to see which of your apps are 32-bit.:

32-bit app compatibility with macOS High Sierra 10.13.4 and later - Apple Support

If you have 32-app applications and are running MacOS Mojave or older, those apps will run fine.

It is only when you upgrade to Mac OS 10.15 "Catalina" that 32-apps will no longer run, and you will have to find out if their developers have released new versions. If not, there is nothing you can do except find another compatible apps that does the same task.

What model year computer do you have? Mac computers have been 64 bit for over a decade. The recent difference is that MacOS Catalina only runs 64 bit apps.