Unclip the front cover
Remove the 3 screws holding the button section to the unit and remove the button section.
Remove the 2 screws holding the board in place. Push the back of the 4 lights either side of the gang connector to the right of the display. This will push the board out from behind and unclip it from the connector.
Remove the globes
Fit the LEDs, they’re very snug and may click into place, once in, rotate them to lock them into place, may be easier to push with your finger nail.
Push the board back onto the connector, plug the unit in to make sure all the LEDs are the correct way around an illuminate. If any don’t light up note which ones they are and replace them turning them 180 degrees. Retry and confirm you’ve got them all the right way around.
Now there are 2 options, you can either remove the light diffuser so the LEDs don’t foul on the inside of the unit (some clever angling of the LEDs will get perfect dispersion), or modify the light diffuser by drilling/melting out the section where the LEDs line up.
Once done, replace the screw and put back together (reverse of taking apart)