Apple introduced the 'natural' scrolling in OS X to partly imitate the experience of going up and down the page as if it were an iPhone or iPad, however it also includes a setting to reverse this system preference in case you want to use classic scroll.
While this feature is offered for most users who want to configure it this way, it may not work in all situations, especially when using a mouse as an input device, rather than the Apple multi-touch trackpad.
In system preferences we can normally change this feature without problems, but sometimes depending on the connected device or its compatibility, it may be that closing these preferences will not save the changes, even sometimes the characteristic indicated in the image above does not appear.
If we cannot find the checkbox to reverse the scrolling behavior, then there may be a conflict between the mouse and the driver software used in OS X. If a proprietary driver has been installed from the manufacturer's website, the best is to check that it is updated to the latest version to avoid these types of problems, if it still does not show or gives problems we can try uninstall third party driver and check if the option is shown again with the default operating system, if the answer is negative, we may have to force the system to show it.
For this we will have to resort to the system Terminal from Applications> Utilities. Once open we will insert the following command:
defaults write -g com.apple.swipescrolldirection -bool FALSE
If we change the value «FALSE» to «TRUE» alternatively, we can check if change scroll behavior when we want to reverse the changes. If when ending with 'FALSE' and pressing enter it returns a value '0' we will have a classic scroll or scroll, if instead we put 'TRUE' and it returns '1' we will have the default or natural scroll.
More information - Use the "Show Magnifier" tool in Preview