If the LNAB (Last Name at Birth) for both profiles is the same - and correct - you merge into the lower profile number, NM.
If the profiles don't have the same LNAB spelling, merge into the correctly spelled LNAB.
If neither profile has the correct LNAB, do not merge them. Instead, correct the LNAB for one of the profiles (effectively a merge); then merge the other duplicate into the new profile (correctly spelled LNAB).
As Eddie notes, you will have the choice of which Text section (Biography, Sources) to keep for the profile that remains.
Images will probably remain also (maybe done by default?); not sure about the Memories section, though. You may want to copy the information in the Memories section to a Notepad (or similar) program, if you have one on your computer/device. You could do the same with the Biography/Sources, just in case!