How to edit a Frame's size?

I have a localscript inside a Frame, in a ScreenGUI inside the player's playerGUI. It is supposed to make the frame's size the player's health. I have it like follows:

-- Part 1
local player = game.Players.LocalPlayer --The local player.
        local humanoid = player.Character:WaitForChild("Humanoid") --Yields (makes the script wait) until the apples object becomes available.
        script.Parent.Size =  {0, math.floor(humanoid.Health)},{0, 5} 
        humanoid.Changed:connect(function() --Connects a function to an event. Known as an anonymous function (as it has no direct identifier.)
            script.Parent.Size = {0, math.floor(humanoid.Health)},{0, 5}  --Sets the Text property of the script's parent to "Apples: " then the apples variable's value. The two dots are used for string concatenation (merging of values to form a string.)
        -- Part 1 doesn't work
        -- Part 2
            if humanoid.Health >= 75 then
                script.Parent.BackgroundColor3.r=(0/255)  
                script.Parent.BackgroundColor3.g=(170/255)
                script.Parent.BackgroundColor3.b=(127/255)
            end
            elseif humanoid.Health >= 50 and humanoid.Health <= 74 then
                script.Parent.BackgroundColor3.r=(47/255)  
                script.Parent.BackgroundColor3.g=(170/255)
                script.Parent.BackgroundColor3.b=(61/255)
            end
            elseif humanoid.Health >= 25 and humanoid.Health <= 49 then
                script.Parent.BackgroundColor3.r=(170/255)  
                script.Parent.BackgroundColor3.g=(157/255)
                script.Parent.BackgroundColor3.b=(82/255)
            end
            elseif humanoid.Health >= 0 and humanoid.Health <= 24 then
                script.Parent.BackgroundColor3.r=(170/255)  
                script.Parent.BackgroundColor3.g=(80/255)
                script.Parent.BackgroundColor3.b=(80/255)
            end
        -- Haven't even tested part 2 but the first elseif is underlined in red saying: expected enf next to function line 4, got 'elseif' 
end)

Thanks.

This is the new script: (It only does the colour change once, and the Size once, then doesn't work)

local player = game.Players.LocalPlayer --The local player.
            local humanoid = player.Character:WaitForChild("Humanoid")
            script.Parent.Size = UDim2.new( 0, math.floor(humanoid.Health),0, 5)
            humanoid.Changed:connect(function()
                script.Parent.Size = UDim2.new(0, math.floor(humanoid.Health),0, 5)
                if humanoid.Health >= 75 then
                    script.Parent.BackgroundColor3 = Color3.new(0/255, 170/255, 127/255)
                elseif humanoid.Health >= 50 and humanoid.Health <= 74 then
                    script.Parent.BackgroundColor3.Color3 = Color3.new(47/255, 170/255, 61/255)
                elseif humanoid.Health >= 25 and humanoid.Health <= 49 then
                    script.Parent.BackgroundColor3 = Color3.new(170/255, 157/255, 82/255)
                elseif humanoid.Health >= 0 and humanoid.Health <= 24 then
                    script.Parent.BackgroundColor3 = Color3.new(170/255, 80/255, 80/255)
                end
    end)