If it's in your phone, it's probably a Micro SD card - they usually come with an adapter to enable you to use it in a "full-size" SD card slot. If you haven't got an adapter, make sure you get one, otherwise you won't be able to use it with your PC or (most) card readers.
The other option is to connect your phone directly to your PC and transfer the music from the SD card to the PC. Then swap cards and transfer the music back from the PC to the card.