29 minutes seems like enough time. If you are from high A gate (A30 or higher) to low B gates (B8 or lower), I would recommend walking, otherwise take the OUTSIDE (relative to the terminal) train from A to B.
If you are walking, there is a large set of escalators just past gate A39 on your right go up these, use the moving walkways to go over to terminal B, then a set of down escalators drops you at gate B4. For all gates other than gates B1- B3 you would just keep walking forward when exiting the escalator.
Note if you are in gates B30-B39, these are in a little "stinger" concourse that sticks out between Gates B29 & B40, look for the sign these leads to these gates.
Should be less than 15 minutes from gate to gate, maybe even closer to 10 depending on your gates. They should keep your seats until 15 minutes before departure, but will sometimes hold a little longer than that if they know folks are on a tight connection.
Good luck.