See here and this station map.
On the Oshiro (Castle) Exit side: Lockers are located inside on the second and third floors and outside to the left of the stairs and escalators.
On the Alps Exit side: Lockers are located on the first floor.
There are only a limited number of coin lockers that can store large-size luggage, and you may need to search a bit to find an open one. There are no storage services or lockers for skis or snowboards.