How to record clearly for a youtube video?

I'm starting up a beauty channel and I uploaded my first video today.
I filmed on my Nikon D5100 and the visuals are fine, but the audio is quite low and sounds muffled on youtube.
How can I make myself sound clearer on the video?
(I was filming in the quiet so there were no noises around me)
Is there a setting on the camera that I can change or anything?

Edit the video

I use a Nikon D5000 which looks to be pretty similar to your camera, and I can tell you, the audio recording capabilities from these DSLRs are horrible. I would recommend buying a microphone attachment for it if you can afford it. (Google "Nikon microphone attachment" to get an idea of what I'm talking about here.) That should make the audio sound crystal clear. As far as I know, there isn't any setting on the camera that will adjust audio quality. Trying to enhance bad quality audio on the computer with software has never really worked out for me either, though I'm not an expert in that field.

I film quite a few of my YouTube videos on a Nikon D5100. As you say, the visual quality is amazing but the sound is terrible. My solution is to use an external microphone. On the D5100, by the hinge for the screen there's a number of inputs. The bottom left is the mic input.

What microphone system you use is completely up to you. I personally use shot gun microphones because I do a lot of non-fiction filming. However if you are intending to record tutorials, where you are simply talking to the camera, the best mic to use is a lapel (also called personal, tie-clip or lavalier). These are the small microphones which clip onto your shirt. For simple talking to the camera they are great because they are so close to your mouth. When I first started out filming with the D5100, I used a Hama LM-09 microphone. I found that considering the price of it, the audio quality is perfectly fine for a site like YouTube. This mic can plug directly into the D5100. Although it is quite an old microphone, the sound quality is just as good (if not better) as the expensive microphone which Nikon sells. The fact that it is an old model simply makes it cheaper to buy. Just search 'Hama LM-09' on eBay or Amazon, and you should find one for under $30.

There are controls for adjusting the input's volume hidden away in the menu. At the bottom of the 'Shooting Menu' there's a 'Movie Settings' section. In there you can enter the 'Microphone' submenus and chose 'Low Sensitivity' I find that is just right for lapel microphones. Avoid using the 'Auto Sensitivity' function. Just make sure you do a full soundcheck before you record.

Hope this helps! Best of luck with your videos. If you need anything else, just pop me an email.