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When I change mine it only takes between 7 and 8 gallons. The filters sit on the plates with 6 bolts (I think there are 6) and they are the short filters. Assuming you are not in a hurry, after you drain the old fluid, drop the filters and just buy the same size replacements.
I measure the oil I removed and refill with the same amount. Checking fluid level with the dipstick is pretty much a useless exercise so after the change is complete I drive it to warm it up and use the touchpad to verify the fluid level is correct. Press the 2 arrows at the same time to enter the fluid level check.
Whatever you do make certain you do not over torque the filter bolts.