question on options

Just a question on hemo
I have had these opps for over 12 months and they are due in march at 20c
If u convert the opps do u go back and pay the full capital gains on the profit
Or if they are converted is the tax calculated at the share price at the time or the cost of the opps + 20c conversion.

Tax = Profit but always looking for the best deal
it may be better to sell the opps and rebuy more shares.

any help much appreciated.