How can I change this green affix?And what crystal to use it?

Remove it using Kryanite then use Amethyst.
note that when using Amethyst it will only give you a few green set affix to choose from
and there are Set affixes you cannot get from it including Set that are exclusive to other classes.
What Set affix are you planning to change it to?

u need to remove it first by using kyanite crystal. and when u want to get another set affix (Green text thing) u need to use Amethyst crystal. Upon applying Amethyst on Item, it will randomly pop up to 6 Set affix. u pick 1 to implant on your item. Before u do that i suggest u read dictionary on Codex first, it will help u in Choosing best set affix depending on your build. and make research. read thread regarding to crystal enchantment. it will help prevent wasting crystal.

Thank you ^^
I’m still doubt about which one to use, but I’m focusing on increasing Ricochet and put Aftermatch wizard intend to further increase the damage of the meteor.
((My english is bad because i am brazillian))