Several responses are correct. You want to turn to the side and up close (but NOT in detail mode), then move your mouse over the bridge of nose until you see the "circular" icon (NOT the cross-bar icon) then pull on the bridge of nose to get the nose tip to turn upwards. See pics below:
Use this icon:
http://i274.photobucket.com/albums/jj255/Pamhamlet/Sims%204%20Photos/NoseTip3_zps1c5c0644.jpg
Not this one:
http://i274.photobucket.com/albums/jj255/Pamhamlet/Sims%204%20Photos/NoseTip4_zps1ff170ed.jpg