What you'll need to do the job:
socket wrench with socket to fit drain plug and cap to fit oil filter, drain pan, funnel, and contact or brake rags.
Oil is essential. If it isn't changed often enough particles of dirt will collect in the oil and as they circulate through the engine will cause damage. Old and dirty oil can also break down and cease to be a protective high-heat and intensity lube. Every 3000 miles is a good standard for changing a bike's oil and filter.

Prepare to change the oil when the engine is warmed up (but not hot) so the oil is runny and drains easily. Underneath the bike is the drain plug. Place the oil pan underneath the bolt and loosen with a socket (or hand-held) wrench. Try not to let the bolt fall into the oil pan when you take it out. Once the oil has drained, wipe spray off threads of the drain plug bolt with contact or brake cleaner, cleaning off dirty oil to ensure a tight seal. At this point you can replace the washer to make sure the seal is tight (unless you have a double shoulder bolt with washer built in). Then replace the drain plug, being careful to match the thread of the bolt, by hand until it seats and then turn it about 1/4 turn with the socket wrench to tighten. If you force the bolt, it will strip the threads and hence will leak; if you over tighten, you'll have a tough time getting the bolt undone to change your oil the next time.

After replacing the drain bolt, move the oil pan underneath the filter and unscrew it. A little more oil will probably come out when you remove the filter. On the new filter, rub some clean oil on its seal before you put it on to ensure the rubber is pliable and will lock the seal. Screw the filter on until it is hand tight. Never over tighten because that will squish out the rubber seal and/or bust the seal and maybe even dent the filter, all of which mean leaking.