Thanks Paul, Jocko Culzean and Olduser1 for your speedy replies.
The spark plugs arrived today so if my daughters Jazz is of the type you mention, then I think I should be capable of changing them. (One of my cars from years ago was a Hillman Imp, if anyone can remember this contrary vehicle, it's when I learnt how to work on vehicles!).
Interesting about the cabin filter but something I will bear in mind. While I really like this Jazz, I feel that it may be using more fuel than it should be, so I would like to eliminate all the causes of this. It could also be that the Jazz may have a smaller tank.
I read with great interest someones link on this site, a very learned engineer's many paged article on the benefits of using eight spark plugs, (something I thought was reserved for the old V8 engines!), and I would have to agree that it may give both better performance and fuel burn. I am not sure if the new Jazz's have eight or four plugs.
The fuel filter may be another item I should look at, as these can get blocked.
The car itself has 77,000 miles on it and drives well. I would seriously consider getting one myself
Anyway friends, many thanks for all the advice and Culzean, for the detailed instruction on plug removal and replacement.