Crash on version 1.7.10

Already reported around 10am 18/03/2015 but since discovered that "user account" is running on minecraft version 1.8.3, and works, but for some reason "miles bate" account is attemping to run on minecraft version 1.7.10 and then crashes. I do not know why this has happened but could be the problem. How do I get rid of 1.7.10 and go to 1.8.3