You can’t rename Presets in PolyNome, but you can save a copy with a new name.
To do this, tap the disk icon in the top right and “Save As” then choose a new name.
This will create a copy of the Preset with your new name. You can then delete the original.
Be warned that deleting the original will delete any Practice Events associated with it.
Copies of the original Preset in Playlists will not be affected.
The reason that Presets can’t be renamed is that Practice Events are tied to the original name of the Preset, as are copies in Playlists.