Pontecimeter of the Audi A4 97 accelerator pedal

Very good
I need to change the poteciometro of the accelerator pedal of my Audi A4 19 TDI of 97, the new piece costs € 450 and in a scratch they give me for € 30 but the workshop that I carry has as a rule does not use scrapping pieces, the scrapping gives me a guarantee of three messages, you could help me and tell me how the piece is changed, since I am desired because I can not allow a expense of 500 in 500 and peak. A car of more than 14 years.
If you could help me, I would appreciate it.
All the best