There are several options for membership renewals. You can use the:

• Auto renewal feature available when you set up the membership page which will automatically renew the member and charge their credit card on file. 
• Membership Auto-Reminders to send a link automatically to members based on their membership expiration date  to renew their memberships themselves using your membership page.
• Membership GM Mail Merge Templates to create letters to mail or email members to renew.
• Email Marketing and Direct Emails to send members links to renew their memberships.
• Advanced Constituent Portal renewal link feature which becomes at a set interval from their expiration date so they can renew themselves using your membership page.
• Renew button on a constituent's Memberships tab to manually renew a member.