When a member has a current membership and an "upgradable" membership type, they can upgrade their membership type with an Upgrade order.
For example, a member may currently be a Student, but during the membership season, may get a job and become a full member.
In this situation, an "Upgrade" button is available in the Membership Details.
Click this button to start an Upgrade order. The steps to complete an upgrade order are similar to an onboard order.