what size tires?
 

I currently have 700x38 sized tires right now. I wan to go smaller, what will fit on the rims? The rims are 622x19.

If the 19 is the actual interior width, you could go down to 700x28s. However you'd probably be better off at 700x32s.

What do you hope to gain with these smaller tires?

Typically, exterior width is about 5mm wider than interior.
You can pretty much go as small as your exterior width, but I feel that's an absolute minimum and should stay at least 1mm wider.

You should be fine with 28's.
My hybrid came with 35mm's, which were total "slugs". I initially switched to 28mm's and it made the bike accelerate so much better and was easier rolling, it made the bike fun to ride.
I've since built a narrower set of wheels and use 25mm's.

Defining a tire's performance strictly by its marked width is missing the point regarding the variations possible in tire construction and weight.

There are heavy, sluggish 28's, and light, responsive 38's (or 42's if you include 650b variants). 25's will almost always be lighter, but not necessarily better rolling, and unlikely to be as smooth riding. Here's my favorite source for light, smooth, and "fast" (but not cheaper) fatter road tires:

Compass Bicycles: Tires

Frequently suggested as a tire that is a good compromise between light, smooth, wide, decent flat protection and less expensive are Panaracer Pasela, especially in the folding, PT, Kevlar bead version, or the similar T-Serv and Gravelking models.

http://www.amazon.com/Panaracer-Pase...913836&sr=1-12

Type of tire will make a bigger difference than width.

A heavy, sluggish 28 will still be "faster" than a heavy, sluggish 38 for relatively smooth pavement.

Factory hybrid tires in the 35-38mm range tend to be heavy & stiff, giving excellent flat protection at the expense of quicker acceleration & rolling resistance.
Within a budget, you pick your poison. Faster, lighter, but more prone to flats OR flat resistance, but not as light and nimble.

Higher priced/quality tires can give a bit better"choice" of fast, light and/or flat protection for your use, within the various constraints.
Many of us don't want to spend $50/tire though.