Changing up the workout?

I am 5'9 1/2" I weigh 163. I am trying to burn enough fat to build a nice six pack and put on lean muscle. My BMI is around the low 20's and my BF% is around 12%. I now do 3 days a week full body lifts(60-75 mins) and 3 days of cardio(30-45 mins) I have heard that my workout is too long and I also hear you get better results if you let your muscles rest and split up by doing 2 muscle groups a day.(M- legs and lower back, W abs and upper back, F arms and chest) I am also wondering how many exercises per muscle group(how may bis, tris, shoulders, legs, back, etc....)