For Sky+ to work you need to:
Upgrade the LNB on the dish (it needs to pick up 2 Sky signals)
You need an extra cable from the dish to the Sky+ box (or a twin cable) - So you can record one program while watching another (or record 2 programs)
I believe you also need a new Sky card.
I think you need to go through Sky to get the new card etc, but if you tell them your dish is in a dangerous position they may pass it on to an independant anyway.
When I upgraded to Sky+ the Sky guy came but saw my dish was on top of my garage and refused to go on the garage roof. Sky arranged for an independant to come out and fit it.