Lagers and ales are defined by the kind of yeast they use- two different species of organism (ales are Saccharomyces cereviseae while lagers are S. Uvarum) as opposed to just different strains of the same species, of which there are many.
Lagers require fermenting at very low temperatures (around 50F) with very large amounts of lager yeast, followed by a short warmer ferment (the diacetyl rest) and then a very extended period of cold-conditioning called lagering, which helps to remove many of the off flavors and aromas created by cold fermentation, as well as develop the flavor.
Ales prefer warmer fermentations (mid 60s F generally, but obviously this varies).
When you frement with a lager yeast at ale temperatures, certain strains of yeast can produce a pleasant fruitiness, and we call some of these beers steam beers, or common beers.
Nottingham is an ale yeast, so regardless of what temperature you ferment it at, it will be an ale. Though, to be clean, nottingham really prefers the low temps- you should aim to have it be 60F at all times. Your kit is just called a lager because that's sort of the flavor the people were going for, and a lot more people know "lager" than "blonde ale" or "kolsch" or a dozen other styles the kit doesn't actually fit into.
Anyway, read the stickies on brewing, know them well, and then toss your kit directions out the window. Any more questions you can probably just put in this thread and get answers.
Good luck, have fun, and RDWHAHB!