How say: correct behaviour; become good again.

[Wai_Wai]

How to say: correct behaviour; become good again.
Say one did something wrong in the past. Now he realizes it is wrong and learns from the mistake. ""He will correct his behaviour"" and ""become good again."" <-- What is the common expression in written AND spoken English?
[as many common options as possible]


My idea is:
Written (formal):
I will mend my way
start life again with a clean slate/sheet

Spoken:
{no idea}

[Tdol]

Reform