I have already added a charm in juju charms store. Now I want to remove from the charms store. Can anyone explain how to do this?
There is a subtle difference between the official Juju Charm Store and charms in the personal name space.
Once a charm has been accepted into the Juju Charm Store by the review process it is maintained by the community and can not be removed from the store.
If however you have a charm in your personal name space (lp:~username/charms/ubuntu-series/charm-name/trunk) you can delete it from Launchpad.
If you own the branch and are logged in, you can delete the branch by clicking on "Delete branch" button. The next screen will warn you that Branch deletion is permanent. and ask you to confirm.
I think this is really answered in Jorge Castro's comment: