To replace the sprocket bushings on a Gomoto GT125, first, remove the rear wheel by loosening the axle nut and sliding the wheel off the axle. Next, take off the sprocket by unscrewing the bolts that hold it in place. Remove the old bushings from the sprocket and install the new ones, ensuring they fit snugly. Finally, reattach the sprocket to the wheel, secure the bolts, and reinstall the wheel onto the bike.