The specification proposes a signal processing method for changing an operating mode for configuring a PPDU in a wireless LAN system. More specifically, a change in the operating mode may be carried out during a time interval known to both a transmitting station and a receiving station. The time interval during which the change in the operating mode is carried out may be explicitly signaled or implicitly notified. For example, in case a change to a new operating mode is requested during a transmission opportunity (TXOP), the change in the operating mode may be delayed until a subsequent TXOP, and the new operating mode may be applied during the subsequent TXOP.