Identify the clips. The plastic of the top cover is a different color from the plastic of the base. You can identify the clips from their color (should be the color of the top cover. Here, they are black).

When you've identified the clips, pull them outward/away from the center (see image) to release them.

You can use any small tool but the plastic may be a bit soft so do this carefully if don't want to wear the clips out.