Thank you for your first post and a warm welcome to the Nokia discussion forums.
So just to clarify since you updated your internet browser, whenever you open this application its runs a lot slower?
There are a couple of things you can try. Firstly try clearing the cache. To do this select Options > Other options > Clear the cache.
Also you can try a soft reset (Please remember to back up your phone) by typing *#7780# and then giving it a try. If not then you could try a hard reset by typing *#7370# (Please remember to back up your phone first!!!)
Furthermore you could also make sure your firmware for the phone is the latest. You can check this by connecting your phone to Ovi suite and checking the phone is on the latest update.
Hopefully one of the above solutions should get you browsing happily again!
Let me know if any of the above helps.