This week the 6 month Libor rate is 2.62. Assuming that the index will be close to that on the date when they figure your change, the bank will add 5.520 to that number and get 8.14. So your new rate should be somewhere between 8.25% and 8.5%.
The monthly principal and interest payment on $235,000 at 8.5% (based on a 30 year payment schedule) is $1807.15.
Keep in mind that these numbers are approximate. The 6 month Libor rate could change between now and the effective date for your change. You can keep track by checking out
LIBOR index and other major interest rate indexes