Removing meta fields after plugin removal

Hello,

We have decided to use another plugin as this one no longer meets our needs. However, after removing the fields in the back end editor and also deactivating the plugin, the meta fields are still present in the back end. I have moved the data to our new fields, so I would like to remove these fields but cannot seem to work out how.

Please advise ASAP how to do so, so I can clean up the clients back end!!

Beth