The Current Project tab gives a detail view on your currently loaded project, with a nice pie chart. It shows you at a glance how much space individual elements of your project need for caching; such as: the timeline preview rendering cache, proxy clips, audio and video thumbnails.

Here, you can selectively delete only some cached data by simply clicking on the corresponding trash can buttons.

To remove all cache data for the currently loaded project, clip on the bottom trash can.

Finally, when you click on the link which is left to the bottom trash can, the folder containing the project cache will open in your file manager.