can't switch my king with rook

I often want to switch my king with rook, but don't know how to do? Can someone help me?

Ok if u haven't moved any piece that's rook or king u click king and rook

Yeah tried that, perhaps if I haven't moved any rook? But that shouldn't be right though

Cause I tried to click both and it's just or king or rook to click

You click your king and move him 2 spaces left or right. If it is legal, you castle.

They don't switch. When you castle, the King goes two squares towards the Rook, and the Rook goes to the square that the King crossed.

Click on the King, move it two squares towards the Rook. The Rook will automatically move to the proper square, without being touched.

Hi Blueemu, LOL  We call it here rokade and in Dutch we say 'omwisselen' so just plain for switch . >< but sure 

Thank you Lagomorph and Jayden for your help xx

At chess.com you can also drag the king on top of the rook, and it will be interpreted as castling (as long as all the gametechnical requirements are met to allow castling). Doing it that way makes misclicks less likely (most particularly, the type of misclick where you accidentally move your king only one square).