Changing an event to a later time can be called "pushing it back":

Sorry, I had to push the meeting back. A lot of people weren't going to be able to make it at that time.

You can also use the phrase "push (something) back to (a new time):

Could I push my appointment back to later that afternoon?

The opposite is "pushing (something) up":

Originally we were going to do it on the 21st, but I decided to push it up to the 19th.