Wont give me the option to transfer songs to the playlists that i made before getting premium

[CCmarie17]

when I first got spotify I didnt get premium for a long time...i probably had like 5 playlists...but then when i got premium and tried to add songs to those playlists it wouldn't give me the option. But still lets me listen to them...so i jus want to be able to put them in my existing playlists instead of making new ones and starting all over. Help!:)