change a number when another changes too

I am  modifying the “StarExplorer” game theached at “getting started”, and I want to increase lives when the score reaches (for example) 1000

I don’t know what syntax I shoud use, but it shoud be similar to this:
 

local function increaseLife()

    if ( scores = 1000 ) then

        lives = lives + 1

        livesText.text = "Lives: " … lives

    end

end

and after, learn how to give more lives each multiple get acheived ( like 2000, 3000, 4000, 20000)