How can I fix my Honda HRB 475 petrol lawn mower?

I have a petrol lawn mower model HRB 475. The rotary blade goes round but slowly and doesnt cut. The clutch adjustment has been altered but it appears the clutch is slipping. How do I renew the clutch plate. I wish to do it myself as I cannot afford the extortionate prices of the implement repair shops and private mechanics. Thanks Dave