Depends...

If you are on a visual approach, tell him "terrain in sight, but thank
you for asking."

If you are on a published (non-visual) IFR approach (IMC or VMC),
and...
(1) you are in IMC, and below the MDA or step down, get above the
published altitude immediately.
(2) try reducing your descent rate as you approach the MDA or step
down alt; ie go to 500 fpm for the last 300ft. You will set off few if
any terrain alerts that way, as opposed to driving right down at 1000
fpm and then levelling off in the last 100ft.

Make sure you do not descend out of the MDA towards a landing, even
with the ry in sight, unless you have reached the VDP if one is
published, or reached your own (calculated) VDP if one is not
published.

Calculate your own VDP as follows:
Take the HAT, and divide by 10. ie, if HAT = 400, HAT/10 = 40
Set the time from the FAF to the MAP into your timer, such that it
will count down to and reach 0 at the MAP.
Your VDP is when the timer shows HAT/10 seconds left. ie, HAT = 400,
HAT/10 = 40; do NOT descend out of the MDA until the timer reads :40 or
less.

Gene
CFII, MEI, ASC