Adding more sources to nodes?

Hello.

So I have myself a server setup, Lands of Dragnar
realms.randemgamor.co.uk

Now, It's pretty much vanilla but I want to tweak some things...

I know it's possible but I can't remember how...

I want to change the yield of a resource node... for example instead of a stone resource node giving 250 stone total, I want it to give say... 500?

How is this possible please?

Many Thanks