How do you multiply the size for ParticleEmitters?

Ok, so I am trying to replace the Fire inside of a Handle with a Particle Emitter, but the scripting for normal Particles is different for Particle Emitters, and I don't know much about them.

I think I have this part down:

                local fire=sp.Handle:FindFirstChild("Lightning")
                if fire~=nil then
                    fire.Size=NumberSequence.new(0)
                    fire.Enabled=true
                end

But what do I do here?

                    local fire=sp.Handle:FindFirstChild("Lightning")
                    if fire~=nil then
                        fire.Size=(percent*extrasize*0.5)
                    end

Please help!