I am entering a tournament in 4 weeks. Should I change my diet in any way? Would it assist me at all?

Not enough to go on. What is your diet now?

As Justice points out, some more info would be helpful.

addition to what you're doing now (in general terms) the big question for me is what do the weight classes look like and do you need to make a weight? This, and the time frame leading up to the event, can mean some radical changes, or none at all, it varies greatly.

With 4 weeks out, what you can do is limited a tad. For instance, you won't effect any performance changes based on the change in all likelihood, although depending on your current fitness level you might. However, 4 weeks is plenty of time to drop off a weight class or two depending on how they are structured.

There are a few bad food habits that make me feel sluggish, so I wouldn't say there can't be any effect.

I think the only time you should "change" your diet for a tournament would be if you are trying to make weight either up or down. If that is the case, 4 weeks to change is way too short a period of time to do so healthfully other than a couple of pounds either way at most. Other than that, eat as healthy as you can all the time.

A change in diet this late in the game won't help unless like mentioned above your trying to drop a few pound to a lower weight class. And I mean a few. You should look a cardiio that with the biggest thing you can change in four weeks. I prefer an eight week training camp for any type of competion that way I get my weight in check and boost my cardio so I'm peaking on the week of the competion.