Bicycle Tutor

Bought a new Dawes sheila for my wife... 3 chain rings on front. Will shift between low and middle chainring, but cannot get to move to largest. Have tried low and high adjustment screws, but must be doing something wrong..
Any suggestions?

i was just adjusting this ...put chain in largest in back and smallest in front, make sure its clicked all the way to smallest chain ring. then loosen the cable with allen key...adjusted the low limit as needed and then tightened the cable again. switch to the smallest in back and largest in front. if it doesn't want to go to largest chain ring, then the high limit screw is too tight so you need to loosen it.
please correct me if i'm wrong...just want to be helpful! i'm sure either dave, UK or joe will help you as they helped me!

Tried what you suggested...still does not want to even move to the big chain ring. It is as if the does not have the travel to get it there.
Thanks for the suggestion though.

i listened to alex's tutorials first...but also looked at other videos like this which were also helpful.

What kind of shifter is fitted to the bike?
If the bike has been bought from a LBS then take it back for rectification.
Otherwise disconnect the cable from the front mech' and see if you can move the derailleur the full amount by hand.
Pull the cable end, by hand, and check the movement of the shifter.
Set the system up as Cure says with assistance from the videos.
Start by setting the derailleur, in the outermost position, to just clear the big ring, by about 2mm, and inline with it.
Re-attach the cable and work from there. You may have to re-postion the cable if it's not right in the first place. Make sure the "stops" aren't restricting the movement of the derailleur by undoing them a good few turns.
With the cable adjuster, set up the throw to get the chain moving over the rings.
Use the derailleur "stops" to stop the chain from dropping of the inner ring or overshooting the big ring.
If you still can't get enough movement then pull the cable (under the the front downtube) by hand to see if that helps.
If it does then suspect the "shifter" ...