To remove or separate by cutting (as when removing the stitching in a garment, removing a vine in one's way, etc.).
The -an imp. focuses on undoing s.t. in order to alter it; whereas the -un imp. focuses on just removing s.t.
Remove the stitching in my pants (in order to repair them), they're way too tight.
Remove the stitching in that sack of cement so it can be poured out quickly.