Can I adjust the arms on my spectacles at home by myself?

At own risk. Speaking from personal experience trying to adjust your glasses yourself usually results in bent or broken frames. It takes a little time to get to the store but I would recommend going back to where you bought your glasses and have them adjust them for you.
Maybe. If the temple material is metal be careful not to kink the arms or they can break. If they are plastic, they usually need to be gently heated and formed to prevent breakage. We have a glass bead bath that slowly and evenly heats the plastic to the core prior to adjustment.