Bicycle Tutor

Can anyone explain how to change the gear cable on these shifters or piont me in the direction of a diagram

I'm assuming these are "road" shifters?
Shimano tech' sheet:-
http://techdocs.shimano.com/media/techdo...http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_6C80D_001/SI_6C80D_001_En_v1_m56577569830
Basically-
Operate the gear lever into the number 1 position. (small rear lever and high gear) (pull on the cable if disconnected)
Pull the brake on and look at the outer side of the lever bit and you will see a small 4mm hole. You won't see it until you pull the brake.
Now if you push the gear cable the end should pop out of this hole.
You can only do this with the gear ratchet in the No. 1 position ( small sprocket)

Have managed to fit new cable however there is no progression from one gear to the next it keeps returning to the lowest gear I think I may have damaged the mechanism there is no click on the gears as the lever moves up.

Did it work before you changed the cable?
Squirt some release oil (WD40)? inside the mechanism.
Work it a few times and it may release.
The ratchet could have seized.
You may be able to strip the unit down but if you do then be very careful with the parts.
I don't think you can get spare parts for Shimano?

it did work before I disconnected it but not very well as though there already was a problem with it