If you use the Drupal Flexslider module or any other implementation relying on the jQuery slider plugin, you can easily change the (default) settings by editing jquery.flexslider.js.
Edit the .js file and search for "//FlexSlider: Default Settings". As you can see below, you can change all the default settings such as "animationSpeed" and "slideshowSpeed" in this section. If you are using a minified version (jquery.flexslider-min.js) don't forget to update it!
Below the default settings you find other parameters related to usability, controls, etc. which you might want to change too.