I am going to pick up my hybrid giant city escape w later today and am worried about the size! I have been ordered a medium but on any size guides I can find it says that for my height (5'4) I should be S? Can anyone advise? I'm sure it will be ok to swap at bike shop but I want some idea in my head before I get there because it was them that ordered the M? Its so difficult to be sure :-( (if u couldnt tell already, I am new!)