The Freemasons fraternal organisation has existed for hundreds of years. The Masons have a system of internal beliefs, practices and expectations. While rumours and film clichés have circled the Masons and enshrined them in a sort of dangerous mystery, the truth of the matter is that leaving the Masons is a fairly straightforward process.
Write a letter detailing your desire to leave the Masons. Sign and date this letter.
Deliver your letter to the Secretary of your Grand Lodge.
Complete whatever requirements there are for exiting the lodge in good standing. In many cases, the lodge will issue a "demit," which simply means that you met your obligations while involved in the organisation. A demit can also help you to rejoin other lodges or attend events, depending on each lodge's individual practices.
Stop paying your membership dues once your leaving has been made official. Some members choose to simply stop paying their dues and stop showing up for meetings, though this is considered a less desirable way to leave the lodge.