That happens sometimes. The reason is unclear. After waiting 15 mins it is safe to turn the phone off and then restart. Check that it shows the new version .72 in Settings > About product.
If there is trouble in turning off the phone then the forced procedure can be used: press both the vol up key and the power key down. Keep them pressed until you feel the vibrator play 3 times (this should happen in 20-30 seconds).