Do it yourself is the best. Need a long wrench and spark plug socket. Different car has different socket size, so I can't recommend in this post. Easiest way is to bring a new spark plug to hardware store or auto store when buy the socket.
I like changing it yourself, because you know how the old spark plug looks like. For example, if you drive 100,000 km, and it is 50% cover by carbon deposit, then you know you should change more frequent. Like wise, if you it is just a little burn (dark brown fire burn due to normal combustion), and clean of carbon or oxidation, then you do not need to replace the plug.
I highly recommend to use more expansive plug, or sharp tip plug, e.g. platinum, or V-Power. They will last longer. Mine driven for 100,000 km and still clean.
You can use
NGK Spark plug, NGK Spark Plug wire, NGK Platinum Spark plug for High Performance and Racing. to look up your model. Please note that newer car are started to use platinum, e.g. 2003 Honda Accord and newer are using Iridium plug. So my recommendation only apply those who drive older model.