I do mine every 30,000 k's as I don't travel much, that's about 4 years for me. If you doing a lot of driving every 80 to 100 thousand k's.
When you say easy well that depends on your skills and knowledge, there plenty of how too on U-Tube I wont post it because I get bullied over posting them, I find it easer to explain through a video as I learnt how to do thing by observing not reading, my writing isn't up to standard's so its much easer just to post a video some times. To me its simple the hardest part is removing the filter seal as you have to be careful not to damage the walls the rest is easy.