How do I change the text of a gui via script when something specific happens?

Why your code only works once

It is only ran once so the 1st result will always be the value of sugar.

What you need is to add a changed event so when the value of sugar changes the Gui is updated.

local sugarObj = game.Workspace.Partscan.Sugar

sugarObj .Changed:connect(function(newVal) -- this is the changed event for the sugar which gives the new value as a parameter

-- set the new value
game.Workspace.Partno.SurfaceGui.Frame.Sugar.Text =  "Sugar " .. tostring(newValue) .. "/1" 
end)

This is only an example, hope this helps

How to improve this script

Currently there are no checks to there is a possibility of parts being nil

Hey Kitorari,

Ok so basically what you want to do is use game.Workspace, it will help. And you are using numbers with integers (but that isnt the real problem I dont think).

Value = tonumber(game.Workspace.Partscan.Sugar.Value)
SugarLabel = game.Workspace.Partno.SurfaceGui.Frame.Suger

if Value == 0 then
    SugarLabel.Text = "Sugar 0/1"
elseif Value == 1 then
   SugarLabel.Text = "Sugar 1/1"
end

If this works, accept answer, it helps both of us