You unscrew the screws that are keeping the front of the crib together to the rest. Then you take the place where the mattress lays on and bring it all the way down. I think you might have to unscrew that piece to apart from the crib and screw it in again at the lowest setting... I did mine long time ago. But I'm pretty sure they have videos on YouTube
What brand is it? I have a delta 4 in 1 and all I had to do was take the front rail off and put the stabilizer bar back on. Her bed is pulled up to my bed so that we can still co-sleep but she's in her own bed while I'm in mine.