The header above the door indicates a bearing wall. If it is a bearing wall you will have to change the header,bigger and longer, it will want to have 2 studs under each end and raised as a pocket door rough is higher. You will also need to see what the new studs will be landing on. Is there a bearing wall below this and is there something below the new studs. If there is a bearing wall there you will want to solid blocking on top of that wall to support the floor below your new studs and you need 2 studs below each side of the door.
A lot depends on what exactly this header is carrying, anytime there is a header the load is carryed all the way to the foundation.