Tap the Erase Message switch in the pop-up menu (earlier versions of the iOS may have somewhat various options in the menus, but they're similar enough that it shouldn't be puzzling.
Kpatụ bọtịnụ Ihichapụ ozi na nchịkọta nhọrọ (mmalite nke iOS nwere ike ịnwe nhọrọ dị iche iche na menus, ma ha yiri nke ahụ ka ọ ghara ịdị mgbagwoju anya.