Upgrading MacBook memory?

Hi,

I want to upgrade the memory on my MacBook. It currently has 4GB.

- It is a white 13-inch Late 2009 MacBook

- 2.26 GHz Intel Core 2 Duo Processor

- 4GB Memory (the memory has never been upgraded before as far as I can remember); 1067 MHz DDR3

- Model Identifier: MacBook 6,1

After checking the memory installation guide on Apple's site (MacBook: How to remove or install memory - Apple Support), it claims that with my model, the maximum memory for it is 4GB. However, after checking an online shop that sells memory upgrade kits (OWC), allegedly they tested the Late 2009 model that I own to trial for support of maximum memory, and it can apparently support 8GB...

From this I'm not sure if I really can upgrade my memory or not, since I've read mixed information that the maximum my model can support is either 4GB or 8GB; I don't want to end up making a mistake purchase so I have to ask, what is the actual maximum upgrade for my MacBook model? Also, is a 16GB upgrade out of the question? (It seemed that way, but just to make sure if it's possible or not..)

Thanks very much!