Remove the mattress from the crib frame.
Remove the crib's front rail by following the instruction manual for your specific crib. Many cribs are held together with screws that can use an Allen key for removal.
Slide the mattress rails to the lowest position.
Place the mattress back onto the frame.
Attach toddler bed rails to the crib frame, if desired. Most rails and cribs have predrilled holes. Line up the holes and loosely screw 38 mm Allen bolts into each rail to hold them in place. The bottom of each rail has a metal L-shaped hook that slides under the mattress.
Cover the mattress with sheets and bedding. The same bedding you were using with the crib will still fit.