Ok, so. There are a lot of ways to do recolours. But since you're learning pixelling, do it manually. I'll do another lesson on techniques for doing these things quicker later on.
So. We are going to take this:
And make him blonde. Yeah, I'm starting easy.
So. First off, download the image and open it in GIMP/Photoshop/Whatever you have. I'm using gimp, so sorry if my language is alien to you, I'll try and speak basically.
Now then, choose a colour for your darkest shade. Mine is HTML a19300. Select all pixels with the same colour as the darkest colour in the hair and fill your whole selection with your colour. Mine came out like so:
Now repeat the process, making your way up the colour scale.
New colour: HTML bcab00
New colour: HTML d2c000
New colour: HTML e4d100
New colour: HTML edda13
Assignment: Taking the same sprite, change the colour of the jumper. Post your end result and all the colours you used. Make the jumper whatever colour you want.