1) It's been forever since I've used an Nvidia card, so just explore the Nvidia control panel until you find where it asks about power saving vs performance.
2) Open the Start Menu and type Power Options. It should pop up with just what you want.
3) Fresh installing drivers is a little more complex than the two methods above. Instructions below.
How to fresh install Nvidia drivers:
1) Download DDU. The Download links are towards the bottom of the page.
http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
2) Open the Start Menu. Open the Power Menu, hold Shift while you click Restart.
3) Blue screen with large buttons appears. Troubleshoot>Advanced>Startup Settings and click Restart.
4) You'll get a list of available starting settings. You're looking for Safe Mode (usually the fourth option). If 4 on the num pad is not working for you, try 4 on the number row above the alphabet keys.
5) Run DDU and remove display drivers.
6) Restart normally, no more need for Safe Mode.
7) Download GeForce Experience for seamless driver installation. When it asks to create an Nvidia account, I used my email address and I haven't gotten a single piece of junk or spam.
http://www.geforce.com/geforce-experience
8) Install display drivers. Restart to confirm changes and finalize the installation. This restart may take longer than a usual restart, this is normal.
9) You can now delete the GeForce Experience setup file you downloaded as well as DDU. They have done their jobs, you don't need them anymore.