The Settings panel is under File > Settings on the Roblox Studio ribbon bar.
Using the settings panel one can change many of the settings in Roblox.
The settings panel is divided into categories on the left, with settings on the right. Settings cannot be changed in-game. When you do change settings remember to restart Roblox.
All settings are Lua Objects and can be accessed with the settings() function. However, you cannot use the function in a normal or local script as it is a protected function. The table below provides links to most of these objects' API except for the Studio setting, which does not appear in the API.