I cant change the size of a textbutton through script?

To change the X value of a Gui:

YourGui.Size.Scale.X = 1

From the look of it your script will possibly not work (I'm not quite sure), Instead do this if your script is not located under the Gui.

-- If your script isn't located in the "StarterGui" do this

local localPlayers = game.Players.LocalPlayer
local playerGui = localPlayers:FindFirstChild("NameGui") -- The name of your gui. 
local settings = playerGui.Settings

settings.Size.Scale.X = 1

However if it is a child of the Gui then

local settings = script.Parent
settings.Size.Scale.X

To change a gui's size <----

settings.Size = UDim2.new(1, 0, 1, 0) 

Fix for your script (Hopefully)

-- Player Variables
local player = game.Players.LocalPlayer
local playerUI = player:WaitForChild("PlayerGui")

-- Gui Variables
local settingsAncestor = playerUI:WaitForChild("Settings")
local settingsChild = presettings.Settings
local controls = settingsChild.Controls
local graphics = settingsAncestor.Graphics

local textButton = script.Parent -- Changed graphics to textButton

textButton.MouseButton1Click:Connect(function()
    graphics.Visible = true
    controls.Size = UDim2.new(0, 150, 0, 28)

end)

Your script is a bit messy, and I can't tell which gui you wamt the size yo be changed, also you didn't pay attentiom to what I've written about and didn't evem bothered to modify your script. Here, hopefully will fix it