Most universities have different criteria for working out your overall final grade - you need to refer to your handbook to find out. However, as far as I know (and in my own experience) you don't officially get a grade as such for each year - if it's something you're bothered about, you can add up all of your module marks, divide then by the number of modules takes and you'll get your 'average' grade, which I suppose would be your grade for the year (that's assuming you're taking individually assessed modules, I'm not sure what you'd do if you're not )
Is it not online somewhere? My uni has all of this kind of stuff on the website, under something like 'policies and procedures' or 'examination and assessment'. Have a look at the duller parts of the website lol.