All compilation products specified implicitly or explicitly by the GNAT project file (*.gpr file) can be removed using the project cleaning menu defined by the Project menu and the contextual menus of the Ada Project Explorer and Navigator. Specifically, the object files (*.o), "ali" files (*.ali), and executable images (e.g., *.exe on Windows) can be removed.
The menu entry is named "Clean Current Project" and is actually two submenus: one to clean the currently selected project root, and one to clean the root as well as the "tree" of projects imported by the root project. (Imported projects are those named in "with clauses" in a project's GNAT project file.) These two submenu entries are shown in the following figure: