Is it Windows Mail or Windows Live mail..
If windows live mail go to add remove and highlight windows live essentials and press delete.It should open up and ask which program you want to repair or delete,Just click on Windows Live mail and press delete.[ Now not sure if that would delete all your saved mail or not but I would not think so].
Then just install windows live mail again.
Well thats how it works with W/7 so should be the same with them all.
If Windows mail I suppose there should be an easy method of removing that as well.
But best to wait till someone can give you better advice.