If you can duplicate the same dirt/growing medium I'd leave one and remove 4...planting the other 4 into small seedling pots. Or consider using the same dirt divided into 5 parts and placing them all in smaller individual pots. Right now the roots are small and discreet, thus easy to separate if done carefully. Later, you'll have more of a tangled mess but would still be separable if done slowly and carefully. As you probably figured out, you could have planted them together but they should have been placed far apart, possibly in a slightly larger pot.

Wait for them to get their first sets of leaves, after the cotyledon have fallen off, you can submerge the whole pot into water and separate them with minimal damage.