330 brakes will give you enough braking power if you pair a quality rotor with a performance brake pad.
Putting 330 brakes on your car is pretty simple. If you've ever done brake work to your car, you were pretty much half way done with the swap. If you havent done brake work on your car before, its pretty simple if you plan ahead and have the right tools on hand.
There should be conversion threads that will give you all the information you need, but basically you need 330 calipers, rotors and carriers. (And maybe brake lines, someone please verify!?)
Your 325 caliper comes off, the carrier comes off and the rotor comes off. Install a new 330 rotor on, bolt the 330 carrier on, and bolt the 330 caliper on.
The most cost effective path is to find the 330 calipers and carriers used. Then you buy new 330 sized rotors and brake pads. With the brake pads, there are tons of threads on pads, but you basically do not want a pad that focuses on advertising it is a low dust pad. Low dust pads generally do not bite as well as other pads. Look into Hawk brake pads....
Pair that with a OE quality rotor as well. You can buy a original style rotor or you can consider buying 330 rotors that are either slotted, drilled or both. Again, some searching around should give you the info you need to make a decision.
Finally, flush your fluid out with a good brake fluid. I recommend ATE Super Blue for that.
2009 E92 335i Alpine White/Coral Red
2007 E92 335i Sparkling Graphite/Black
2000 E46 323i Steel Blue/Grey