1 i dont know, serial number c1mnckdfty3 if that helps
2 i dont know
3 i upgraded in my house. I dont know the precious one.
4 there was a hard drive problem which i took to get repaired.
5 i hace never backed it up ( i think)
For #1 and #2, click on black Apple icon in the upper left hand corner. YOu'll then be presented with a menu of items, the first one being "About This Mac". Click on it, and it will tell you what OS you are using. There is a also a Mac model "name" there, but that is not enough. So, on that screen, click on "System Report". On the next screen, you'll see an entry for "Model Identifier". That is what we need.
You can upgrade "at your house", whether you do an upgrade in place, ie, basically "lay the new OS over the old one", or do an Erase and Format of your internal drive, and then a clean, "Virgin" installation of the new OS. But, you need a backup to do that.
Even though you got the hard drive "repaired", I suspect it still needs a good "cleaning", ie, disk cleanup, maintenance, and repairs. But again, you'll need a backup before you do that.