The goalkeeper, like any player, can be substituted at any stoppage of play, with the referee's permission. The important difference for goalkeepers is that they also need the referee's permission to switch positions with an outfield player (outfielders can normally interchange amongst themselves, but the 'keeper is a special case).
Chat with our AI personalities
You can make up to three changes during a game. The number of substitutes varies across leagues and competitions, but no matter how many players are sat on the bench, you can only make a maximum of three substitutions.
A maximum of 3 players can be subsituted in a football game. A player is subsituted when he is injured, tired or underperforming or due to tactical reasons.