Deleting a wrong uv-mapping ?

After some hours, I am beginning to understand one or two things concerning uv-mapping. But how do you delete a uv-mapping once you have set one ? because. for example, it is not at the right place ?
Thanks in advance

you uv map again

[press the U key in face select mode with some faces selected]

you can’t delete the uvmapping without starting over entirely, and it doesn’t make much sense to have “deleted” uvmapping either for particular faces but not others

You can delete all UV-coordinates here:
Edit buttons (F9)
under the Mesh tab
the button Delete next to the Texface button