I have a threadless headset and I was able to take off the handle bars, but I can't seem to raise them at all because they're already on the edge of the stem. What can I do to increase the height of the handlebars? I love my bike but the handlebars are just a tad bit low for me; I find myself leaning forward almost too much I think - to the point where I have to raise my head to see what's in front of me. Good for racing ... not so good for commuting.

I have no clue whether the stem can be extended but when I unscrewed the handlebars and pulled on the stem nothing happened.

Specifics: I have a threadless headset with spacers.

EDIT: I found some threadless stem extenders ... all I need is the right headset diameter and I'm good to go right?

You can buy a stem with more rise angle, that's the normal first remedy. I'd only go with the stem raiser/extender if even after putting on a stem with as much rise as you can find, you still need the bars higher.

I would opt for a steeper angled stem as mentioned, followed by a riser bar, and agree that the last resort would be an extender.,, I would even consider a new fork with a longer steering tube if the bike is your long term ride instead of an extender.

What's wrong with extenders? I just don't want to have to "rewire" a new handlebar ... I'm new to bikes and only really know how to do basic stuff like adjust brakes.

Deontologist, having read your two posts above I am having trouble understanding what you are seeing. You shouldn't have to "rewire" for a stem change on a typical threadless setup. I wonder if you either have a single piece handlebar/stem or if you are calling the steerer tube a stem. I only say this because you say you are new to bikes.

Perhaps you can look at one or both of these videos to understand how the stem can be removed and flipped or replaced without replacing the handlebars:

How To Change Your Threadless Bike Stem - Performance Bike Learning Center

How To Change A Stem - Bicycle Mechanics | Global Cycling Network

I am new to bikes. I think I am calling the steerer tube a stem. So can I extend the steerer tube? Thanks btw for the information .

The stem raisers effectively extend the steerer tube. There's nothing really wrong with them, it's more of an aesthetic concern, and it adds a small bit of weight. You don't have to re-tape or re-adjust cables to do a stem swap on threadless stems (unlike older quill-style stems). Watch the videos linked above.

Stem Raisers extend the steering tube, But so does Buying a new fork with an un cut steerer.
The latter is better .. the former replaces the current stem on the fork, then you put your stem on top of the stem raiser.

Raising the bars further than the cables will reach means the cables and housing must be replaced.

Buy an adjustable stem