This may be resolved by transferring the membership to a dummy constituent record and merging it back into the source record (if this is a scenario where there are two duplicate records with two duplicate memberships, begin at step 6 and use the duplicate constituent instead of the "Dummy").

NOTE: this process will not work if the Membership status of one of the Membership records is "Cancelled." Follow the steps here to view the member's transactions, and highlight the "Drop" and click "Delete."

NOTE: this process will also not work if the Membership program allows multiple memberships. You can edit this setting in your membership program to merge memberships by going to your membership program and clicking Edit on the General Tab. Here you can uncheck/check the box "Allow multiple memberships." 
  1. Go to Constituents > Add an individual > Add a new Constituent with only a last name as this is the only required field (this will be the dummy record)
  2. Go to the Membership page of the Constituent with the duplicate memberships
  3. Go into the Membership that is current
  4. Click Transfer Membership
  5. Select the dummy record and transfer the membership
  6. Go to Constituents > Duplicates > Merge two constituents
  7. In the Source constituent field, select the dummy record
  8. In the Target constituent field, select the normal record
  9. Select to "Delete source constituent"
  10. Click Merge
  11. The Constituent should no longer have duplicate memberships on their record