To Fire Someone
To Fire
する verb
You are going to untie the person who is in your employ from being employed with you. They are free. This means you fired them, which is why this verb means to fire someone.
かいこする
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
シャークは事あるごとに規則違反をするので、そろそろ解雇する必要があると思います。
Shark has been stepping out of line every chance he gets and I think it’s time for us to let him go.