There are 4 hidden recessed locating lugs inside the round rim. These snap clip the cover on. The first two are about an inch up from where the handle joins the circular part. The only way to release them is to use two flat small screwdrivers and lever outwards the blue plastic cover away from the black plastic body. Use one screwdriver to hold the gap open and the other to lever the cover up swapping the screwdriver process as you work along. As you pass over the top of the area where the locating lug is it will suddenly release and then you can start on the other side. When these two are released you can then lever the whole cover back even more in order to see see where the remaining top two are located and you can then lever these off as well.
Geoff
April 2019