My 4 year old

Skye
I have 2 kids one aged 3 and other aged 4 my 4 year olds behaviour is unbelievable bad I'm scared he will kick off when I meet my partners dad for the first time and I'll have a break down what do I do when he dose something wrong I tell him off or put him on the naughty chair but nothing working any ideas how to turn his behaviour around please (no judging plz)