hi
if the shares are equity, then you can surrender the shares to the company but not entitled to encashment.
if the shares are preferential, then the company on maturity will ask you to surrender the share certificate for encashment.
in such case write a simple letter addressing to the company stating that you are the preferential share holder holding the share certificate no distinctive no and no of shares whose maturity date is so and so and would like to encash the same for which you are enclosing the said share certificate and request to issue cheque/dd in your name.
other views are welcome