Window is slower than before

[javvad]

Dear all,

Recently I have bought Samsung omnia pro b7320, i updated its windows
6.1 to 6.5 using Samsung pc studio. After updating, my phone is slower than before. I'm using the lightest desktop themes but still it’s slower. is it due to the updating or is there is any other reason.
Secondly how can i restore its default
can anybody tell me the procedure of "hard reset" for Samsung Omnia.