I FINALLY got around to do this DIY but since I didn't want to ruin one of my favorite denim shirts, I went and bought a cheap one at a small store and luckily, the operation was successful!. ...This DIY is as simple as they come so if you are feeling adventurous, here is what you need and the step by step:
*Special fabric bleach in powder (if you can't find it, use normal bleach)
*Gold buttons (make sure they are the same size as the buttons you are replacing)
1. Remove all the old buttons from the shirt (thats if you decide to change the buttons like I did)
2. If you are using the special fabric bleach, follow the instructions on the package to get the color off the sleeves. I had to heat up the water and pour the powder into the hot water.
3. If you are using normal bleach, pour the bleach (Carefully, otherwise you will stain your clothes) on a small tub with a little bit of water (enough to cover the part you want to bleach).
4. Make the sleeves wet BEFORE you get them in the pot or tub.
5. Once you have your sleeves wet and on the water with the beach, leave it there and move it occasionally so that the color disappears evenly.
6. See the color disappear and get it out of the water when you are happy with the shade. (you can leave it until its very light or maybe a lighter shade of blue).
7. Rinse it and dry it (I washed it again with fabric softener to get the bleach smell off it)
8. If you decide to change the buttons as I did, stitch them once its dry.
WHY DONT YOU TRY IT AT HOME? ;)