Stop attending pledge events, especially if you have already decided to leave the process.
Ask a brother in the fraternity about the possibility of re-pledging in the future. If you decide to try again another semester, the fraternity may have special rules -- for example, you may need to start the process over from the beginning instead of picking up where you left off.
Remember that you have no formal obligation to the fraternity. However long you have been pledging, you have the freedom to walk away without owing anyone an explanation.
Give the fraternity brothers confirmation that you are leaving the process, particularly if you are near the end. This removes any doubt they may have about your possible return and gives other pledges the opportunity to compete for your spot.