How to Adjust Your Mouse through OS X Yosemite
The Mouse System Preference pane in OS X Yosemite is where you set your mouse tracking speed, scrolling speed, and double-click delays. If you use a notebook Mac, you won’t see a Mouse icon in the System Preferences application unless you have a mouse connected, or have at some time in your Mac’s life, connected a USB or Bluetooth mouse.
The first item in this pane is a check box: Scroll Direction: Natural. If scrolling or navigating in windows feels backward to you, try unchecking this box.
Moving right along, here are the features you’ll find in the Mouse System Preference pane (if you have a mouse connected):
Move the Tracking Speed slider to change the relationship between hand movement of the mouse and cursor movement onscreen. This slider works just like the slider for trackpads.
The Double-Click Speed setting determines how close together two clicks must be for the Mac to interpret them as a double-click and not as two separate clicks. Move the slider arrow to the leftmost setting, Very Slow, for the slowest. The rightmost position, Fast, is the fastest setting.
If your mouse has a scroll ball or scroll wheel, you also see a Scrolling Speed slider, which lets you adjust how fast the contents of a window scroll when you use the scroll wheel or ball.
If your mouse has more than one button, you see a pair of Primary Mouse Button radio buttons. These let you choose which button — left or right — you use to make your primary (regular) click. Conversely, the other mouse button (the one you didn’t choose) becomes your secondary (Control or right) click.
This is a setting many lefties like to change. Set the primary button as the right button, and you can click with the index finger of your left hand.
Right-handed defaults are chosen here, so the left button is the primary click and the right button is the secondary (right or Control) click.
Changes in the Mouse System Preference pane take place immediately, so you should definitely play around a little and see what settings feel best for you.