Just got Mac desktop. Already needs updates but...

Ok so I just bought a Mac desktop a week ago and it already needs updates....I live in Tahoe and have a MIFI....with 12G for data......already went over my data limit and the updates still did not finish.....when I try to update pages, it goes from 1 hr & 46 mins to 21 mins....or 196 MB to 3.6 KB then back down to 196 MB....what the heck????? so I used all my data & it didn't even complete???? I am certainly not proficient in tech but I do know how to click on "update"...what is happening???