Cleaning...
The side-trim has metal brackets fastened inside, carefully undo the screws and scrub the panels & brackets clean with plenty of hot soapy water. remove any marks with magic eraser (you will need to re-polish the panels if you do). when you refit the screws
DO NOT OVER-TIGHTEN them as the plastic pillars they fasten into will break!
This is why I strip down any cab I get - I found all of this loose inside this cab....
To re-assemble reverse the process - however I do have some tips.
When you fit the white front marquee retainer, fit the two middle screws first - then fit the edge ones as the extra flex you have makes lining up the screws simpler, also refit before putting the side trim back on in case you drop the screws.
Fit the top pair of speakers loosely so you can tweak them so no gap above monitor.