when the tutorial begin,i want to say this is very easy tutorial..and this tutorial not only for change the demon to the blue,but u can change all object colors..first i write the tutorial for GIMP,because a lot of request for GIMP software tutorial..
-GIMP
-First download the following materials

-after downloading..open both image with GIMP
-then klik the demon image and click colors>hue>hue +180



-next step..klik that demon picture again..click Image>copy (ctrl+c)>and paste to the ice background with pressing ctrl+v like the picture below..


-now what??u have finished making the ice demon using GIMP :D
-then if u want add something to the demon..i have some object for you..








-Good luck..i hope the tutorial useful to you :)