Combining Multiple Rows Into One

I have two spreadsheets of 27,000+ rows each.

Each one consists of user data for each time they logged onto our systems. The problem is that there is one row for each login. There are anywhere from 1 to 20 (or so) rows per user. I need to turn that into a spreadsheet with one row for each user.

In theory, the problem shouldn't be that difficult. Each user has a unique user ID, and the only math that's required in the merge is a simple adding of numbers from three columns to give a single total for each user.

So far, the only workaround I've been able to come up with is using the subtotal function based on the unique user ID which will at least isolate each user and total up their usage statistics. But it still leaves me with the problem of deleting the now uneccessary extra rows by hand, and then pastin the data back into a new sheet. Using vlookup, I think.