Don't have to worry about it until you have to sell the property. When you are selling, your lawyer will handle it without any extra charge.
If you do want to discharge it now. Go to the bank and tell them, you have paid down your mortgage and you would like to discharge the mortgage. They usually charge your administration fee (most banks charge $200.00, some banks $300) and discharge fee ($70:50). If they charged $70.50 discharge fee, they will take care of everything; if they don't, they only give you authorization, then you have to visit Land Registry........but pretty simple.