Places to start:
Criticism of postmodernism
Articles to broaden your understanding:
What is metamodernism?
Quirky, Tone and Metamodernism
Beyond Postmodernism. Putting a Face on Metamodernism Without the Easy Clichés
The Death of Postmodernism And Beyond
Postmodernism is dead
Help with putting it all together:
Here is also a great site that will hugely help with your revision. It looks back to Modernism, to Postmodernism and forward to Post-postmodernism and compares then to each other.