When you reach certain Warlock levels you learn additional Invocations, as shown in the Invocations Known column of the Warlock table . If an Invocation has prerequisites, like a certain Warlock level, you can learn it at the same time that you meet any prerequisites it has.

When you gain a Warlock level, you can replace an Eldritch Invocation you know with another Invocation of your choice.

Below is the list of Elder Arcana that a Warlock can learn. If an Arcanum has a prerequisite, like a certain Warlock level or a certain Pact Focus, you can learn that Elder Arcanum at the same time that you meet any prerequisites it may have.