Easy to install. However, that really depends on the person. If you can do simple do-it-yourself installs, it is easy. (You can search for the installation instructions online and read them to see if it is something that is doable for you.)
It is a 500 gallon filter, so depending on how many people are in your household, the replacement frequency will vary. You can guestimate how many gallons of purified water you would use in 1 week or 1 month. Then divide 500 by that number to get the number of weeks or months of use. For example, if you use 10 gallons per week, you would change the filter about every 50 weeks or about every 12.5 months. (500 / 5 = 50 weeks. 50/4 = 12.5 months)