A method is provided for decoding data in a wireless access system. A user equipment (UE) receives a higher layer signal including an indication that 256 quadrature amplitude modulation (256 QAM) is to be enabled. The UE further receives, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS). The UE also receives data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH, and decodes the received data using the MCS represented by the index field. The UE has a first MCS index table supporting up to 64 quadrature amplitude modulation (64 QAM) and a second MCS index table supporting up to the 256 QAM.