It happens to me that I have imported several textures or materials or else, but then may be I changed those in external program and I have to reimport because it seems not to update theones I did already import and so I have clones over clones and stuff is starting to clutter the whole space , so how I can do to selectively eliminate stuff I do not want anymore from my assets?
Right click on the assets and choose Open in Explorer (for Windows).
In Explorer delete the asset(s)
Repeat as required then close Painter
Next time you open Painter it will be gone from the shelf
I would use the File-> Clean method along with the Resource updater unless you want to delete the files outside the project and inside it. The Render Updater can currently be accessed via the lowest icon on the left hand side menu (looks like a file with a recycling icon).