Hi all , I just completed GF1 .Chord changing is becoming a little bit easier now but am still struggling with strumming.I can strum perfectly well D D D D strumming and changing chords slowly but when I try to up the speed a little bit DUDUDUDU I keep hitting the 6th string sometimes when I try to change G to C ,G to Am and D to C .Any help ,advice or excercise method will be much appreciated .