You can feel free to rename or delete a playlist, except for the default one - "My Playlist".

For Android users

1) you can rename or delete the playlists under "My playlist".

2) click to enter a playlist - the "three vertical dots" icon on the top right corner - Playlist Settings.

3) in the Playlist Settings page, you can rename or delete it.

For iOS users

1) you can rename or delete the playlists under "My Playlist".

2) click to enter a playlist - the "three horizontal dots" icon on the top right corner - Playlist Settings.

3) then you can rename or delete this playlist.