Once the screws are removed the pump body can be split open. Use a metal spudger or a thin flat head screw driver and do this slowly - do not just bust it open as you may damage parts.

NOTE! You do not need to separate the pump case all the way down to the bottom where the stem meets the red swivel for the mop head. The screw here needs to be losened off enough for you to be able to separate the main body above it.