Power: You can replace a power with another power of the same type (at-will attack power, encounter attack power, daily attack power, or utility power), of the same level or lower, and from the same class—a 5th-level attack power for another 5th-level attack power, for example, or a 22nd-level utility power for a different 22nd-level utility power.
You can’t replace a power that’s a class feature (such as a cleric’s healing word or a warlock’s eldritch blast) or a power gained from a paragon path or epic destiny.