It depends on what key your original is. If you wrote in F and want G, you have to remember your base key was C, so when you transpose, you need to go up 2 half steps from C to D in order to move your F song to G. If in that scenario you were to say "transpose to G", it would move your song up a whole 5th because your base key was C even though your chord progression was F, Bb, C, etc....

Count semitones and transpose that way. Think about it is "I want to move this up 2 semitones" rather than "I want to move this to G" and you'll be fine.