You will need the Volvo prop wrenches to remove and install the props. The drain plug is just ahead of the prop and just below the prop shaft. The tools are around $30 such as these:
http://www.ebay.com/itm/Volvo-Penta-OEM ... vW&vxp=mtrUse a short 2x4 or other block between a prop blade and the anti ventilation plate just above the props to keep the props from turning while you loosen or tighten the prop nuts. Below the prop shaft is the drain plug. It takes a 3/8ths inch Allen wrench. This plug looks like a bolt about 2 inches long with an O-ring in a groove on the shank. Trim the outdrive down to at least level or farther down to help with draining into a pan. Be sure to check the first little bit of oil for water, foam, or other issues. Don't confuse water coming from inside the gear case from cooling water coming out around the gearcase. Remove the cover on the back side of the upper half of the outdrive. This should take a 3/8ths socket for the 3 bolts. Remove the plug on the back side of the upper drive. This should take a large flat blade screwdriver. Also take the Dipstick out of the top of the out drive. This should take a 5/8ths inch wrench. Removing this plug and dipstick will help vent the outdrive to allow the oil to drain properly. When the outdrive is completely drained, trim the out drive to level and you can slowly pump approximately 2 1/2 quarts of 75W90 Mobil 1 or similar gear oil back into the outdrive. The outdrive is full when oil comes out of the plug on the back of the upper section of the drive. Reinstall that plug, check the level with the dipstick, and install the dipstick. This will reduce oil draining back out while you disconnect your fill hose and reinstall the plug. Reinstall the props and you should be all set.
You might check this link to a service manual:
http://boatinfo.no/lib/volvo/manuals/sx ... ve.html#/4