The Amarna Revolution refers to the radical changes to Egyptian religion, art, architecture, politics and foreign policy instituted by the Pharaoh Amenhotep IV, who changed his name to Akhenaten, and moved the capital of Egypt to present day Tel el Amarna, naming it Akhetaten.
Amenhotep IV was the son of Amenhotep III, during the most powerful part of the 18th Dynasty, where Egypt's empire was at its height. Prior to his reign, the Egyptian religion consisted on thousands of gods and goddesses, the most powerful 'king of the gods' was Amon. The temple of Amon at Karnak was the biggest in Egypt, and the priests were correspondingly very rich. The pharaoh himself was considered to be a god-king. Egyptian art and architecture was very standardized by this time.
Amenhotep IV changed his name to Akhenaten, and declared that all other gods are false, and that the one true god was the Aten, the sun's disk. He began to deface and destroy temples to other gods, and built a great temple to Aten at Karnak. The priests were displeased, and Akhenaten moved the capital from Karnak (Thebes), to the barren place in middle Egypt, where a whole new city and temple and palace were built.
The Amarna revolution included radical changes in art as well, with a more naturalistic style of art introduced. The Bust of Nefertiti is an example.
Akhenaten also didn't care about Egypt's empire, and the holdings in Asia were lost during this time.
The Amarna Revolution was short lived, however. It began with Akhenaten, and ended with him. When young Tutankhaten, who changed his name to Tutankhamon, became the new young pharaoh, he reinstated all of the old gods and restored things to the way they were before.