If all other shifts are normal, it's more likely a sticking 1-2 valvetrain. To change fluid, you need to drop the pan. You will also want to replace the filter while you're in there. The trick to dropping the pan is to do so without bathing in ATF. The best way to do this is to use a large drain pan and loosen the pan bolts in a pattern, starting from the front. Generally, the fluid will begin to drain from the front of the pan as you loosen the bolts. Once the bolts are loosened, remove all but one bolt on each side close to the rear of the pan. Then, while supporting the pan with one hand, remove the last two bolts and gently roll the pan towards the front, allowing the remaining fluid to pour into the pan. On some installs, the rear crossmember restricts access to the rear pan bolts so that you have to raise the rear of the trans slightly to get those bolts. On these units, I generally remove those bolts first, then move to the front and follow the pattern I detailed earlier. The filter just pulls loose by hand with a little twisting back and forth. The filter to case seal may be either rubber or rubber embossed steel. Using a large screwdriver, you can carefully pry it out. Do not dig the screwdriver tip into the case or you,ll create an internal leak.
Recognize that the 700R4 holds about 12 quarts of fluid. Much more than the pan holds. When at rest, the fluid is way above the edge of the pan and will begin to drain as soon as the pan seal is broken. In a pan drop service, you'll replace about 5 quarts of fluid. You can have a shop that is so equipped perform a fluid exchange, using a machine that is designed for this. I do this here at my shop. We run 16 quarts through the trans via the cooler lines. In reality, with intermixing of old and new in the trans, it probably actually replaces about 7-8 qts of the total fluid. But it's better than nothing. Remember the Lubeguard. Lubeguard is a great product that doesn't have any affect on seals and doesn't try to be a fix all. It's just a combination of friction modifiers and lubricants that improves valve operation and reduces wear of bearings and bushings.