One of the easiest jobs really, but arm youself with the correct oil, oil filter and sump seal first. You may also need an oil filter strap wrench.
Find out what sort of sump plug your car has, and make sure you have the correct socket / allen key / square key to suit.
The car engine needs to be warm to allow the oil to flow easily, taking the carbon deposits with it.
With the car on a level surface, remove the sump plug, catching the oil in a suitable tray at the same time. Recover the sump plug, clean it and fit on the new sealing washer if necessary.
Turn your attention to the oil filter. If it is a spin on canister type, like a can, you may need a special strap wrench to unscrew it anticlockwise. Once it starts to move, oil will spill from here too.
If it is the paper element type, these are held within a plastic housing and come complete with 2 rubber O rings. Again, the filter top is unscrewed, and the paper element lifted out. Oil will spill everywhere.
When all of the oil has drained from the car, fit the sump plug, don't overtighten it. Wipe the engine down where oil has spilled.
Replace the oil filter with the new one. If its a canister type, spread some fresh oil around the rubber sealing ring. If possible, fill the filter up with fresh oil - dead easy if its vertical, awkward if its horizontal and impossible if its upside down. Tighten the filter by hand, then 1/2 turn more with the wrench.
If its the paper type, look how the old one comes off, clean up what you can, replace the O rings, smear oil on them and reassemble.
Take the dipstick out, and wipe it clean.
Add new oil through the oil filler cap until the level is recorded on the dipstick, put the dipstick back in and put the filler cap on.
Start the engine and check for leaks.
Stop the engine and check the oil level again. It will have gone down as the filter filled up. Replenish the oil up to the maximum on the dipstick - no more.
Check the sump plug and filter again for tightness, check the level after a day or so. Job done!
A Haynes manual (or similar) will also help you.
John