I recently finished the siding on another side of my house and we plan
to not just add shutters,but we also want to trim the top with these
sharp lookin viny headers that are available. Can they installed on top
of the vinyl now that l already done the siding. Is there anywhere i
could possibly find an instruction that i could visualize,maybe
something downloadable?

It will have to be flashed. But vinyl siding is easy to remove and
replace; instead of coming up with some grand plan to avoid removing
the vinyl, which is the RIGHT way to do it, I would remove it and put
your header up, flash over the top of the header, then reinstall the
siding. You can put it back right in the same places except trimmed
short and around your new header. Bends and snaps into place easily
(except in cold weather). Doing it this way will also probably be
faster as well as better.

Thanks eDeck, i'll make a note of what you said. I suppose i need to
study how to properly remove the siding.

There's a little inexpensive tool for that; its a 5 inch long bent
prybar to reach under the lip of the interlocking siding and pull them
apart; but i've always just done it by hand. Find an end and push
down and out, once you've got a lip disengaged you can continue down
the seam with your hand and slide it along to detach the whole length.

Before reshaping and reappying the siding around your trim, install the
necessary J trim and/or undersill flashing; see your other openings
(windows, doors) for a sample of what those pieces look like.