According to the Giant website (which may or may not be accurate) the Roam 1 was speced with CST 1272 tires which I can't even find listed on the CST website. I'm guessing that means they're a really low grade tire made specifically for OEM installation.

If you actually want to 'upgrade' without trading one problem for another, suggest you look at a tire in a similar (or larger) size with a high thread count construction, some anti-flat protection built on, a round profile and as little tread as possible.

You're driving a hybrid, which combines some advantages of both a road bike and a mtb bike. If you just end up sticking skinny tires on it you'll end up with the advantages of neither.

Wider tires will give better float on gravel and unpaved trails and tread is really only an advantage on snow and mud. Contrary to popular belief, its not the width of a tire that determines rolling resistance, its the quality of the construction.