Bicycle Tutor

Hi.
My rear changer will not change from first to second. If i click once nothing happens, second click it will go to third gear. I can then change to second. It changes fine from 8th to first.

Have you tried adjusting the derailleur cable?
Wind the adjuster out on the derailleur a bit ( only a 1/2 turn a time ) and see if that helps.

i have tightened the cable but this seams to have made it worse. is it possible the dérailleur is worn out?

Check out Alex's guide:
http://bicycletutor.com/adjust-rear-derailleur/
Make sure the derailleur isn't bent / twisted.
It should be vertical as well as inline with the sprockets when viewed from above.
If the derailleur is worn then by getting hold and twisting it would show any wear.
There will always be some play in the unit but not much.