wifi problem =(

hey people i bought this blackberry 9700 bold last week
its amazing phone but there is some problem with wifi


when i connect to wifi the internet works ok but after some hours when i open browser it does not respond as if internet is not connected
but my wifi is connected and the interent is also working
i checked other phones and on them internet was also working except on my bb 9700..

when i change the name of router it starts working again but then after some time it stops working
i dont knw wat is the problem
becuse whenever i change the name from my computer of router and search again on bb the network its starts working .

help please

try to upgrade your OS to the latest one.

wat if i dont want to upgrade??