Ren, do you have a relatively older teenager near by? Someone in the 15 to 17 range who is still in school? If you do then ask them if they are or they know a computer guy, I can almost gurantee you they will. One of those guys can take your machine and in a couple hours return it clean, fully updated and protected.
Either that or ask around with friends and find someone if you can. While reinstalling is not difficult, it can be confusing at certain points and small errors can show up that are simple to get past but may trip you up if you let it get you frustrated, and that is normal for someone who has never done this stuff before.
Now if you are really patient and would like to learn something, then go for it, the most important thing is to select the existing partition when it asks you, you want to overwrite what is there, not create a new partition that will leave the old stuff there. You should see a warning that formatting the partition will erase all data, that is a good thing.
Everything else eddo told you is perfect, Dell is a great source for all your drivers and information. It is a good idea to have a second computer around if possible, that way if you get an error you can use the other machine to look it up or to download drivers if your having conflicts for some reason. The ethernet driver is going to be one of the most important because that is how your going to get this machine on the internet to download updates for the OS. I would have that driver if nothing else on a jump drive as the first thing to add because many times the base operating system cannot use a generic driver for that.
Good luck Ren, it is not as hard as it seems if you like puzzles and are patient.
PS
Like eddo said, if this is new for you I would not worry about trying to save any files from the computer, you never know if there might be viruses and stuff in there you also saving and moving. If your on a budget you can send small files in your email to yourself that you want to save but again I would not mess with that, just erase it and start over.