Heat sink gap
The trick to replacing the acrylic panels once everything is installed is to leave the screws that secure the heat sink lose. This allows you to slightly pry apart the heat sink from the case enough to install the panels.
Replacing the panels
Fit the inner panel
Start by inserting the inner panel into the slot of the right side heat sink (fixed side) ensuring that you also clear the bumpers.
Secure the inner panel
Now make sure the other edge slots into the left side heat sink. You may need to gently force the heat sink away so the gap is big enough and make sure it also clears the bumpers.
Fit the NET
As with the inner panel, fit the NET, it should be easier as its slightly smaller and more flexible. Make sure its sitting flush on top of the inner panel.
Fit the outer panel
As with the inner one, begin by inserting it into the slot on the right side heat sink and ensuring is also clears the bumpers.
Secure the outer panel
Again, ensure there is enough gap by gently prying the left heat sink away from the case so that the edge of the panel clears the side then fits into the slot. You may also bend the acrylic panel to help with clearing the bumpers.
Repeat all these steps on for the panels on the other side.
Secure the heat sink
Finish the assembly by securing all 4 screws. Make sure all the panels are correctly aligned in the slots otherwise it will be difficult to close and may damage a panel.