Replacing the engine air filter on a Ford Escape (1.6L and 2.0L Ecoboost shown) is very easy. There are a few plastic panels and covers in the way. With a couple common tools and this guide you'll have it changed in a few minutes flat.

This article shows a 2014 Ford Escape 2.0L Ecoboost (turbo), but the 1.6 uses the same intake and filters. This should apply to similar years like the 2013 and 2015 models.

You should check your air filter approximately every 10,000 miles. When it the filter material is mostly covered in dirt, it's time to replace the filter (or clean it if you have a reusable filter like K&N)