You can get different keyboard layouts on Google Play. Download whatever one you want to use and it should allow you to automatically install it when you download it. If not, or if you get more than one and want to change them up, you can go into "Settings" and then "Keyboard & Input Methods". In here select the keyboard you want to use and make it the "Default". If it doesn't automatically change to the new keyboard, try restarting the phone and then it should be active.
NOTE: This will not effect keyboards that are app specific. So any app that has its own keyboard layout, etc., will not change.