Exploring a Shift from Paid Membership to Advertising Monetization

Hey all, here’s a question regarding shifting monetization strategy, from paid membership to advertising. I have 1500 members, of which about 20 paid members. I have received many requests for job postings and classifieds, and as the paid membership has been stagnant, I want to switch to advertising only. How do shift those premium members to “normal” members, and how do “stop” the current recurring paid memberships? Has anybody else done this?