Macbook RAM upgrade ADVICE

Hello, thanks in advance for any help I receive here, this is my first post!!

I've the below Macbook;

MacBook (13-inch, Aluminum, Late 2008)

2.4 GHz Intel Core 2 Duo

2 GB 1067 MHz DDR3

NVIDIA GeForce 9400M 256 MB

Its updated to OS X El Capitan 10.11.1 (15B42

I've removed all photos and videos and music to a hard drive to help it run quicker but I'm having no joy. My friend advised to upgrade the Ram

Apple say that this model can take up to 4GB Ram, but I've read on a few forums it can actually handle 8GB

My questions are, would it be worth upgrading the ram and will I noticed a difference?

Is there an Apple recommended UK website I can order from?

Can I just follow the instructions on the Apple site on how to change the RAM?

Many thanks!!!!