Remove all the bedding including the mattress, sheets, pillows and toys from the 4-in-one crib.
Remove the front rail of the crib using the Allen wrench or screwdriver.
Turn the crib on its side. Place the mattress spring rails securely in the lowest position.
Turn the crib back upright. Fix the guard rail to the right or left of the opening left by the removed front rail. Secure the guard rail using the Allen bolts and the Allen wrench, or the screws and the screwdriver, without over-tightening them
Replace the mattress on the mattress spring, and make up the bed.