If you want to make more you need to scale and scaling probably means starting an agency and turn from programmer to manager/director.
Another approach is to charge more. If you have many clients, it is possible that some of them are willing to pay more than others.
Finally, granted that I don't know anything about your situation, stop and think: do you really want to do this? I mean, 120k/year in most European cities is a very good income.
If you want to make more you need to scale and scaling probably means starting an agency and turn from programmer to manager/director.
Another approach is to charge more. If you have many clients, it is possible that some of them are willing to pay more than others.
Finally, granted that I don't know anything about your situation, stop and think: do you really want to do this? I mean, 120k/year in most European cities is a very good income.