You could do a simple cleansing, as well as a "breaking the cord" ritual/spell.
Each is very simple: for the cleansing, some of the easiest ways to do this are by taking an herbal or a salt bath.
As for breaking the cord, you would need a representation of yourself, one of Lucifer, then tie the two together with a cord. This cord represents the deal you made with Lucifer, and when you cut this cord, you have broken the deal. Afterwards, dispose of each representation away from the other. You can toss them into different streams, bury them in different places, or burn them at different times. The idea being that you two remain separate.