How to find and remove a word from a string?

The title says it all. I've looked on the WIKI and it's not really explained too well which is why I've come to you guys, you seem to make sense of things.

But I've made a Squad Gui in which players can join a squad etc... But when they leave their name is still left their in the squad members box. All wanted to know is how to find a specific word in a string of the players name's I've got and how to remove that word. I can do the rest myself.

Thanks!