Changing an air filter is one of the simplest of all the servicing tasks, and on many cars you need no tools at all, as the air filter housing lid is held on with clips.
Some cars require the use of either a screwdriver, or small socket (commonly 7mm) to undo the bolts which hold the lid of the air filter housing in place.
You may also need to remove the hose going into the housing if it obstructs the opening, this again will probably require a small socket, or screwdriver.
How to extend the life of your car's air filter
As with all service items it's not wise to extend the life of the air filter, particularly as they're so cheap. You can (if desperate) remove the air filter and brush off any of the larger particles in an attempt so prolong its life – but considering their minimal cost, it's really not worth the effort.
How long should a car's air filter last?
As part of the service schedule most air filters should be replaced at 10-12k or 12 month intervals. Replacing them sooner will do no harm, but unless it's visibly dirty there's not a great deal of point.
Having said that if you regularly drive in dirty, dusty conditions – say on building sites, or down a dirt track you may want to consider replacing it more often.
How much does it cost to change an air filter yourself?
Very little. It's likely you'll already have the correct tools (everyone has a screwdriver!) and a replacement air filter will cost between $10 and $20 in most cases.
Some specialist cars may be more expensive (particularly ones which use foam air filters as opposed to paper) but they're never going to break the bank.