customizing the eyes of Yukino?

is it easy to take off the eyes of Yukino manually to change the the eye color or does it require some tools in order to take them out?

Check out this guide.

http://aquilla429.co.uk/how-to-guides-for-dollfiebjd-care/how-to-removechange-eyes/

Plus there is this fourm: http://www.dollfiedreams.com/viewtopic.php?f=21&t=811

does it require to put eye putty on it?

Yes, because it won't stay if there isn't any.

  Nightmare Tea said:

Yes, because it won't stay if there isn't any.

 

where can i buy them?

I just use regular white blu-tack to place the eyes

Some doll stores do sell eye putty, but most people that I know either use white tack, silicone earplugs, a kneaded eraser or a hot glue gun.

 

Do NOT use super sculpy, fimo or other similar modeling clays because they can damage the eyes and the doll to a state of disrepair.

 

It is 100% necessary to use something like this otherwise they eyes have nothing to hold them in. I won't repost my tutorial as someone else already linked it, but you are obviously very new to the hobby and I would recommend reading and following it as closely as possible.