You would have to move the apps that are on the current card back to the phone's true "Internal" storage. Any apps downloaded directly to the card would be unmovable, so they would need to be redownloaded and installed again after the change over. Also any other files (music, photos, etc.) would need to be either moved to the phone itself, to a cloud account or to a computer to save them. Then you would convert the card back to "External" storage. Once done, remove that card and insert the new one. Then you can again convert the card over to "Internal" storage. Once that is done, then you can move the apps that were put back on the phone itself back over to the new card, or download apps directly to the card. You can also, if you chose to, move the files you backed up to the card.
However, before going through all this, make sure you view the specs for the phone you are doing this with. Phones have limitations on the size and speed of card they can use. You don't want to go through all that to then find out you got a card that is the wrong size (storage capacity) or wrong speed for your phone.