In WLM, click on Mail (bottom left).
Then right-click on the account you wish to remove, select "Remove Account".
This will also remove any messages under that account, so if you wish to save them, move them to a Storage folder first.
My Computer
At a glance
Windows 7 Ultimate x64 RTMIntel(R) Pentium(R) D CPU 3.00GHz6 GB dual channel DDR2 333 MHzNVIDIA GeForce 7800 GTX 256 MB