To move a Contact from one Membership Level to another simply head to Memberships > Membership Levels > New membership (using the green button at the top of the screen).
Select the Membership Level required, select Continue.
User the "Pick a Contact" field to select your Member, Continue.
If your Membership Level has a membership fee, you will need to indicate if the account is paid, needs an invoice or is paying now. If the some of the original Membership Level fee is being counted towards the new level, then a Partial Payment can be recorded.
To Cancel their previous Membership Level, head into the Memberships > Reports
Click on the Number next to the Contacts name.
Click the Cancel button to cancel the Membership Level.