Take out the crib mattress and all bedding.
Remove the two M6 x 40mm bolts securing the foot-end assembly to the side rails with an M4 hex wrench.
Move the foot-end assembly to the side.
Remove the four M6 x 50mm button head hex bolts securing the mattress support assembly to the corners of side rails the with the M4 hex wrench.
Assemble the full-size bed rails according to the manufacturer's instructions. Position the cross arms parallel to each other, then place the top and bottom cross supports between them. Secure the cross supports to the cross arms using bolts. Insert the glides or rollers into the feet of the cross arms.
Screw the top end of the full-size bed rail into the bottom of the head-end assembly, or headboard, using only two of the four M6 x 50mm bolts retrieved from the mattress support in Step 4.
Screw the other end of the full-size bed rail into the foot-end assembly, or footboard, using the two M6 x 40mm bolts retrieved from the foot-end assembly and the side rails. The footboard is optional.