if i change my ip adress will my internet still act the same?

Hi,
I know how to change my ip adress, but will there be anything bad happening when i change it? I dont pay for my internet, my dad does, so i dont want to stuff anythin up.Will the name of my internet change, will i still be with optus? Is it bad if i change my ip adress for my pc? PLs help!
explain 'ports forwarded in my pc'
I have no idea what that means lol
router* oops