You will need to remove this section of the undertray
Undo the fixings - use a 10mm socket
Carefully remove the cover
Don't forget to place a suitably sized receiving tray beneath
With an oil catchment tray in position, use a 17mm spanner or socket to carefully remove the sump plug and fully drain the oil.
When the sump has emptied, wipe clean the sump plug area with a paper towel and fit a new sump plug and washer
Do not over-tighten. Refit the cover