Have a nose on Autotrader or Skoda’s stock locator to see if any are within your willing travelling distance. Email dealer and see if the will hold it for a small deposit why you cancel the one on order.
To cancel, Visit or email the dealer telling the you are cancelling the order for “x” vehicle. Its a simple process.
To change fuel type, just visit the dealer and tell them you want to cancel the 1.5 and go for diesel. This however, may be a problem if your dealer hasn’t a diesel in stock, as no factory orders are allowed.
Be prepared to widen your distance, you stand a better chance of finding one in stock.
The Tarraco is essentially the same car and would beable to place a factory order. Worth searing on Autotrader etc for any avalable stock.