Disconnect all of the power sources to the spa and remove the access panel on its side to expose the pump unit. Close the gate valves if your unit has them or drain all the water from the spa.
Detach the copper bonding wire from the pump's ground terminal and unscrew the two unions that hold the pump inside the spa. Remove the screws that mount the pump to the brace bracket and carefully lift the unit out of the equipment bay.
Unscrew the face plate over the wet end and use a rag to clear the impeller blade of any debris.
Check to make sure the impeller is tightened to the motor shaft by removing the motor cap to expose the shaft. Insert a screwdriver into the motor slot and check to see if the impeller turns while you hold the shaft in place, if it does, tighten it, the impeller should not move without the shaft.
Scrap off any build-up of rust on the motor shaft to improve its operation and use a thread file to remove any debris on the shaft threads. They should be clear so that the impeller glides onto the shaft easily and stops solid at the end of the threads.
Lubricate the impeller shaft with water and replace the pump seal, if needed. The stainless steel side with the rubber doughnut should be against the impeller blades.
Lubricate the rubber cup with water on the ceramic half of the seal and press it into the housing to secure the unit against leaks.
Check the motor shaft for free movement after you finish any repairs to the impeller. The bolts should be tightened and the shaft should be centered; off kilter movement could damage the motor and impeller permanently.
Replace the necessary parts and reverse the steps to reinstall the unit into the equipment bay. Your spa motor should be able to run smoothly again.