I don't really understand the question.. do you mean, how do you go about changing rhythm from bar to bar?
*facepalm*. Rhythm means based on "I got rhythm". Changes is jazz slang for chord progression. It's just a standardised chord progression that is prolific enough to be called a form, like the 12-bar blues.
What should it be called? "Well used and known chord progression based off Gershwin's 'I got rhythm'"? Unfortunately, people tend to shorten things and use slang. That doesn't make it poor or misleading.
The name shouldn't be changed now that it is standardized nomenclature, but the term is misleading. It should have been named "'I Got Rhythm' Changes" so it would be clear that rhythm and timing are not the issue.

However, the stupids have struck again and we are left with a poorly named term.
Read the wiki.

But it's an ABA form I believe. Check the Mile's tune 'Tune Up' for an interesting variation.
Resident Melbournian of the AUSTRALIA FTW! Club. PM the_random_hero or Alter-Bridge to join. Australians only.