I'm currently writing a fantasy novel and its my first piece of work. My chapters currently range from 500 to 3350 words. Is this too much of a dramatic change? Should I go back and pad out some of the shorter chapters? Am I over thinking it, or is chapter length that important? Thank you for your help
Assuming there are no requirements for chapter length you are supposed to meet, I don't believe it matters. Some books maintain a steady chapter length of twenty or so pages (Harry Potter), but I've seen several with a page long chapter, followed by an extremely long one (Inheritance Cycle). Still yet others maintain short chapters throughout (Anne of Green Gables). In my experience, such ranges don't really mess with the pace/flow.
Chapter length is important. Consistency of chapter length is not.
A few ways to use chapter length:
Think of chapters as a pacing tool. All other factors being equal--which, of course, they never are--longer chapters tend to slow the pace, shorter chapters to increase the pace.
The length of a chapter can suggest (perhaps subtly) the importance of the events in the chapter. A longer chapter can give more weight to the events, a shorter chapter less weight.
These two effects often fight with each other.
In my opinion, everything about a novel or other piece of writing must follow from its whole. If the lengths of your chapters follow narurally from the story.you are telling, then those are the lengths they must have. Word count is the wrong way to evaluate writing (unless you write specifically for a certain word count, as in academic or news writing). Let someone read what you wrote and tell you what might be too much or missing. Don't follow the advice of a word counter.
Is this too much of a dramatic change? Unless your book is to be serialized by chapter, it doesn't look like an issue.
Should I go back and pad out some of the shorter chapters? Not necessarily. If a read-through demonstrates that the flow is not how you want it to be, chapter length may be changed, although usually indirectly: you may erase some slow parts, or tighten up some other parts, or put in some dialogs, descriptions or previously removed scenes. As a rule of thumb, what happens on a given chapter and how it is portrayed is the driving force for chapter length. Unless your book is to be serialized, as I said earlier.
Am I over thinking it, or is chapter length that important? You may as well use the chance to get some work done. You can make chapter length important if you give it meaning within your writing.
As stated by @Dale Emery in his answer, chapter length can be used to great effect. I like @what's take on it: "Chapter 10: Paul died." is a very powerful effect, especially if you take care to make all of the other chapters long by comparison.