If you are not bothered by learning the same lessons over and over, which frequently require suffering, then there is no need to change your karma. Keep on going as you are.
However, if you want to resolve your problems and issues, and experience less suffering and more peace in this lifetime, then it is time to change your karma before you exit your present physical body.
Karma affects not just one aspect of one’s life, but different aspects. Everyone may have one part of their life going well while another part is breaking down. For example, someone with good financial karma, as in being successful in their business, could have bad relationship karma. When I say “good”, I mean desirable or healthy, depending on the situation. Saying something is good or bad in this case is just qualifying the situation in terms of what is optimal and what isn’t.
Having good karma in one department does not undo bad karma in another department. You have to deal with each category independently.
That being said, good karma does not protect you from the bad karma of others. Lots of people undeservingly get harmed or killed by others. Good karma only prevents you from having to repeat the lessons of what you already know.
Remember, also, that some unfortunate events have nothing to do with a specific karma. Life has its downs — that’s par for the course. An example is when you’re driving on your way to work and someone hits you. You obeyed all traffic signals and didn’t do anything wrong. Neither did you ever hit anyone else in your whole life, nor did you wish someone else to be hit. Things happen.
What to change is what you CAN change, such as thinking, attitude, perspective, and behavior. Is it time to forgive yourself? Love yourself? Stand up for yourself? Set healthy boundaries? Make amends? Express gratitude toward someone? Show someone you care?