straighten up

verb

1. To become straight, or straighter.

   “2006, American Motoryclist - Jan 2006, Victory's Kingpin goes its own way bank the big cruiser into the first of a series of corners, make a few quick left, right, left transitions, then the road straightens up for a stretch...”

2. To steer straight.

   “13 October 2010, Blackpool Gazette, 'Bad driving' led to biker death crash He said "As I came out of the bend I went to straighten up the car and it just seemed to be carrying on turning."”

3. To sit up straight, to stop hunching.

   “Horse skin smells good. Lay your cheek against his neck and have a good cuddle. Now straighten up slowly again, and sit loosely.”

4. To deal with; to put in order.

   “1994, Mccook Daily Gazette, Jul 12, 1994, Mail Delivery Trying To Get Up To Speed The Postal Service sent a special task force to straighten up the city's problems with a back-to-basics approach”

5. To tidy; to tidy up.

   “The lockers were all standing wide open with equipment and uniforms scattered all over the room, he had left a note under the bottle telling me to straighten up the room, then straighten myself up before coming to work the next day.”

6. To clarify.
7. To start living a reformed life; to adopt a more honest and respectable course of behavior.