Change or Cancel a British Airways Revenue Ticket

[sunshine]

I purchased the British airways ticket that Dan posted 2 weeks ago and may need to change or cancel it. Any ideas if this is possible with BA.

Thanks

[Pesach]

is cardofferu 10 percent off flights  available for a website like priceline or expedia? if i find a lower price on a ba flight can i cancel the booking I made yesterday on my ba account before i booked the better priced deal or do I do a duplicate booking and then cancel the old flight i booked assuming this is in the 24 hrs cancelation  for paid tickets. thanks

[Pesach]

also can i use an evoucher issued from American airlines for the ba website to book on open skies flight?