flight time change

my wife and I were due to fly to Malaga in November departing early a.m from Heathrow . We were also leaving Malaga midday arriving U K at a reasonable time. I have just received an e-mail from BA telling me we now depart UK late afternoon and we depart Malaga late evening. I have found flights from Gatwick on the same day with flight times that suit us much better my question is will I have any problem getting BA to change things for my benefit ?? TIA.