The same person, twice, under two spellings. It happens on an import, and it happens when somebody is added by hand who was already there.
There are two tools and they are for different situations. Pick the right one.
Merge, when both records are real
Use this when both entries have something on them: a match, a sign-in, a payment, a season.
Open Members, find one of the two, and choose Merge. Type the name you want to keep, and pick it.
Before you press anything it shows you what the merge would do. Read that first.
Their whole history moves across. Matches, results, seasons, money: all of it ends up on the one record you keep.
A merge cannot be undone. The dialog says so at the top, and it means it. That is why the preview is there.
Remove, when one record is a mistake
Use this when one of them has never been anything: a typo, a row an import brought in twice, a name that should not have been there.
Remove deletes that record for good. It will not delete anybody who is really in your club, and it tells you who it kept and why. Your members has the detail.
What a merge cannot move
A player's sign-in is their name. That one does not move, so if two people are signing in you merge the names rather than the sign-ins.
Where both records hold a different email or phone number, you say which one to keep. Each field comes from one record or the other, not from both.
Not having to do this again
An import matches people against your register before it writes anything, and step three tells you who it matched. Read that screen rather than pressing through it, and most duplicates never happen.
If one does slip through, Import keeps every list you have ever brought in, each with its own Undo.