How do I change the sky with clicking a button?

Try this! Put this inside a part in workspace. Put this script inside a clickdetector in the part: Part>ClickDetector/Sky1/Sky2>Script

local Part = script.Parent
local Sky1 = script.Parent:FindFirstChild("YOURSKYMODELHERE")
local Sky2 = script.Parent:FindFirstChild("YOURSKYMODELHERE")
local Toggle = false
script.Parent.MouseClick:Connect(function()
    if Toggle == false then
        local Clone = Sky1:Clone()
        Clone.Parent = game.Lighting
        local Other = game.Lighting:FindFirstChild(Sky2.Name)
        if Other then
            Other:Destroy()
        end
    else
        local Clone = Sky2:Clone()
        Clone.Parent = game.Lighting
        local Other = game.Lighting:FindFirstChild(Sky1.Name)
        if Other then
            Other:Destroy()
        end
    end
end)

All you have to do is put two of your skys (put the ID in them too) into the part and put the names in the script! Enjoy!

You could delete and replace the sky with another you have stored somewhere

function OnClick()
    game.Lighting.Sky:Destroy()
    local SkyClone = game.ServerStorage.SkyReplacement:Clone()
    SkyClone.Parent = game.Lighting
    SkyClone.Name = "Sky"
end

Or just set each part of the sky

function OnClick
    game.Lighting.Sky.Top = -- Roblox Image URL --
    game.Lighting.Sky.Bottom = -- Roblox Image URL --
    -- etc. --
end