Your first step is to find an attorney in your area to advise you. Next, inform the landlord that you will be leaving the business and request to be removed from the personal guaranty. If the landlord says yes, you'll want the attorney to help draft the necessary amendments to the lease/guaranty.
If the landlord says no, you'll want the attorney to draft a document whereby the remaining partners agree to indemnify you if the business defaults on the lease and the landlord comes after you. Make sure you do this as part of a coordinated exit plan with your partners.
Nina L. Kaufman, Esq. is an award-winning New York City attorney, edutainer and author. Under her Ask The Business Lawyer brand, she reaches thousands of entrepreneurs and small business owners with her legal services, professional speaking, information products, and LexAppeal weekly ezine. She also writes the Making It Legal blog.