This is usually very easy. If the bed is in sofa format, you need to take the mattress cushion off and reveal the base. This comes apart very easily and needs to be laid out flat on the floor. You can then put the mattress, again laid out flat on top and make up the bed with covers and duvets as required.
Some of the larger futons are heavy and probably require two people to assemble and convert into a bed.
Some of the larger futons are heavy and probably require two people to assemble and convert into a bed.