• Install and initialize the update of one of the Locuses
• Accept the offer to change its main directory:
  
• the app detects the other one and warns of the possible loss of access to the data of the other app after the transfer
  
• select one of the available private folders into which the data will be transferred
• after the transfer, restart the updated app

The updated app detects the other Locus Map in the external storage (removable SD card) but it can not migrate its data automatically:
There are a few more steps to do:

• change the location of the main directory of the second Locus Map from the external SD card to the private folder in the internal storage
• update the first Locus Map and continue according to the instructions above