I just purchased a Cannondale Quick CX3 Hybrid and I assembled it using REI's instruction manual.

I would like to raise the handlebars, but the instructions on this process weren't very clear.

There are 4 spacers already installed, but I would like to increase the height. Do I need to purchase additional spacers in order to increase the height, or does that take it above the minimum insertion line?

That bike has a threadless stem (stem clamps to the steerer), if all of the spacers are below the stem, it seems your only option to raise the bars further would be a different (greater rise) stem and/or bars with some rise in them.

If there are spacers above the stem, these can be moved below the stem to raise it. You will need to re-set the headset preload and tighten the stem/steerer bolts. This is pretty easy to do.

Don't add more spacers, as you will not be able to properly set the headset preload and you will have less of the stem around the steerer, both of which are dangerous.

You can buy a stem with more angle to it that will give you a little more height, but unless you have steerer tube above the stem at it's current position, you can't do much else easily.

Your desire to have more height makes me think you need a different bike. Can you return this one? Might just be you need a bigger size or different model that's a different geometry. Don't buy a bike style, just to have that style. Make sure it's got the geometry you want.

There's no minimum insertion line. That applies to a quill stem or seat post but not to your steering tube.

Is there any sticking up above the top of your stem (with a spacer there)? However much there is, is how much you can raise the stem. If not, stems are inexpensive and easy to change. Get one with a higher percentage rise.

There are no spacers above the stem, so it looks like I will need to look at a new stem.

The CX is a fairly relaxed geometry with a fairly upright posture. That is why I wonder if you got the right size. Be cautious of wanting to sit too upright, because that is just going to put more weight on your butt and then you'll be forevermore trying different saddles wondering why your bottom hurts so much.

Though a stem change isn't going to put you very much higher unless you go for something weird and drastic looking. A shorter stem can do the same, but from the pic, that looks like a pretty short stem anyhow.

Thank you for the advice on this. I'm also trying to ensure that my posture stays upright since I have a bulging disc in my neck. It gets sore after ~30 minutes of riding when my shoulders are too forward.

I will most likely just wait for REI to re-open their stores and then take it in to have the fitting done by one of their techs.

You probably need to rotate your hips forward and straighten your lower back. Have look at this thread: Riding Position Discovery
and try that out before you go in for your fitting.