While merging two member records is not possible at this time, you can follow a few simple steps to accomplish the same outcome using the non-member merge function.
In the People Manager, identify the two (or more) member records you want to merge together and choose one to remain the official and final member record. For the remaining member record(s) you wish to merge to the main record, update the Member Status to Dropped. Once the members have been dropped, return to the Member Status menu for the newly dropped members and select Convert to Non-Member.
If the membership has expired, you can convert the member record to a non-member without needing to mark the member as Dropped first.
Once you drop a member you may need to update the search filters in the People Manager to show Dropped members in the search results in order to find the newly dropped member and convert them to a non-member.
Finally, find the new non-member record by updating your search filter to include non-members. See Merging a Non-Member with a Member or Non-Member.