Trailer Slide Out How Do You Change Out The Boards On A 5'x10' Trailer?

How do you change out the boards on a 5'x10' trailer? - trailer slide out

I have a flat bed trailer 5'x10 'advice and starts to rot. There's no slot for the stitches slide back, should I get a 2x8-fold under the lip? I have no problem from them. Please help!