Should I ask for a submitted recommendation letter to be retracted in order to submit another, stronger recommendation?
You can't "retract" a letter.  This isn't done, and I think it would look weird and somewhat suspicious.  The committee might be inclined to read that letter more closely in case it contains something damaging that you were trying to conceal.  At the very least, it seems distasteful to be "gaming" your professors' supposedly well-considered evaluations in this way.

You certainly can have this other professor submit their letter in addition to the others.  For those schools that specify three letters, it will be up to the committee whether they read all four, or choose three in some arbitrary way.  I suspect that if three letters suggest you're a viable candidate, the committee will be willing to look at the fourth.