Looking to upgrade from the XTI

[taylortx]

Hey y’all! I'm a beginner and was gifted a Rebel XTI and EF 75-300mm lens to get started. I've quickly noticed the downfalls and am trying to figure out my next move. My primary use is photographing birds, so I did purchase a relatively inexpensive 420-800mm lens as well. 

As a beginner, I don't want to spend more than a couple hundred bucks. I don't need the latest and greatest, just something that performs better in low light and has a higher resolution. If anyone has any recommendations, I’d greatly appreciate it!

[Tronhard]

Hi and welcome to the forum:
Oddly enough, I actually still have my copy of the exact same camera, so I hope my observations can be helpful.

The EF 75-300 is arguably Canon's least impressive optic and that is definitely a weak point  (I have no knowledge of the 380-800 you mention).  To get much the same range and a better lens, I would suggest the excellent EF 70-300 f/4.-5.6 IS USM MkII.  It's much better, having image stabilization, a superior build, seriously improved optics.  A while ago I did a review of the choices of 70-300 selection of lenses, and in your case the second lens in the list is the best for you.   If that is too expensive then the MkI version will be even cheaper and is still much better than the 75-300
70-300 Canon Lenses In-Depth Analysis - Canon Community

This would fill in the gap up to the 420-800 you apparently have.

[taylortx]

Thanks so much for the wealth of information, Trevor! So just to be clear, it’s less about having an outdated body with low resolution, and more about the quality of the lens?

Thank you again!!

[Tronhard]

I would say yes. While the sensor is obviously a contributor, I would put the balance on the side of the lenses you choose for it.    I didn't take your post as a suggestion that you wanted to upgrade the body, but if you were doing so that might open up a whole new collection of questions.
You might want to read the following document on the subject of getting gear:
Buying Camera Equipment