How do I fix my ride hight on my 94 Cadillac sedan deville myself, it says...

[Rob]

..."service ride hight"on the dash? On my dash info it says service ride hight and the back of my car is lower then the front can anyone help me and let me know what I need to buy to fix it myself I don't want to go to a shop I wana learn it my self the back of my car don't raise up at all it stays low and it scraps when I drive over speed bumps even up the drive way thanks for the anwsers