A lot of options that affect gameplay can be changed in OpenTTD. Many of these options can be changed from the Advanced Settings window, but for some of them you have to edit the config file, openttd.cfg. Most advanced settings improve gameplay or the interface, while others give you more power in the game.
Changing Advanced Settings
The Advanced Settings window allows you to change most of the available settings from within the game. The Advanced Settings window has a tree-like structure, divided up into the following main sections:
Buttons are green to show the setting is on, red to show it is off. Arrow buttons change the value of the setting like a horizontal scrollbox. Clicking on a patch-line with arrow buttons shown will bring up an edit box, where the desired value can be typed in.Some features that have been advanced settings (patches) in older versions of OpenTTD can now be found under difficulty settings, game options or cheats. Some of them might even have become permanent features that you cannot disable.
Since r14275, the name Patches was dropped in favour of "Advanced Settings" in order to avoid confusion with TTDPatch in general, or patches (in the technical sense) against the source code of OpenTTD often found in the Development section of tt-forums.
Since r14974 the tabs at the top of the window are removed and all advanced settings are listed in a tree structure. This allows for subcategories that can be expanded and collapsed independently. The former tabs (Interface, Construction, Vehicles, Stations, Economy and Competitors) are now top level categories and they can now have subcategories, for example the subcategory Trains in Vehicles.