How to upload a Decal
From Legacy Roblox Wiki
Introduction
This tutorial will show you how to upload a Decal.
Steps
1) Create an image with a program such as MS Paint
2) Save it to your desktop
3) Click on My ROBLOX
4) Click on Decals
5) Click on Create
6) Click on "Browse" (to find your newly created Decal, which is on your Desktop).
7) Click OK
8) Click Create Decal
9) Wait for a moderator to approve your (non-TOS violating) Decal.