To replace a Kubota oil filter, first place a large drain pan under the drain plug, and loosen the drain plug using a wrench. If the tractor has another drain plug, place another drain pan under the second plug, and open it to drain as well.
Next, depending on the model of the tractor, remove one of the engine's side covers to access the oil filter. If the tractor has a front-end loader, remove it too. Using an oil filter wrench, remove the old oil filter from the engine block. Drain the oil in the filter into the drain pan.
Take out the new oil filter, and apply oil at the top seal to lubricate it. Wipe the surface where the new oil filter should fit, and then spin the new oil filter until it's firm. If the old oil is completely drained, take the drain plug, clean it and inspect it for cracks or wear. If it's in proper condition, plug it back in, and tighten it using a wrench.
Measure the amount of new oil the tractor needs, open the oil cap at the top of the engine, insert a funnel and add oil. Afterwards, replace the oil cap, and confirm whether the oil is at the correct level.