I was driving right before the highway and my brake pedal got stuck

The pedal getting stuck is most likely an issue with the floor mat. It sounds silly but if this doesn't happen all the time or only happened once, then I would suspect it is something along these lines rather then an issue with a brake component.

As for replacing the rear brakes, here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors

Plus below you will find the process from the manual on how to replace these as well.

Please run through this material and let us know if you have questions. Thanks