Midterm Upgrades will always be priced as the monetary difference between two Membership Levels, regardless of the membership duration. When processing a Midterm Upgrade, keep in mind that this will not extend the Expiration date on the membership, nor will it account for the expiration date in pricing. 

In order to Upgrade the membership and also extend the Expiration Date, we should click the Memberships button in Daily Sales and then select to Renew the Membership. After, click the Renewal in the Sales box and click Edit at the top. We would then be able to upgrade the level and move the Expiration date. Note that this will charge the constituent the Full Price for this level with no discount.