If this is your first time installing Plato, the easiest way is to get the Plato one-click install package from mobileread.com.
This will install the original Plato and the necessary launchers.
Next, go to the Releases page and download the latest. Unzip to location where Plato is installed (usually .adds/plato/) and overwrite all files. Your settings will be preserved.
The settings are saved in and read from Settings.toml. You can edit this file when Plato isn't running or is in shared mode. You can enter the shared mode by connecting your device to a computer.
You can also edit Settings-sample.toml and rename it to Settings.toml before you first run Plato.
plato.sh has a few settings that you can override by with config.sh (use config-sample.sh as a starting point).
The following style sheets : css/{epub,html,dictionary,toc}.css can be overridden via css/{epub,html,dictionary,toc}-user.css.
Read THEMES.md to learn about themes, which provide a quick way to set several reader settings at once.
Read CSS_TWEAKS.md to learn how to tweak CSS styles for individual epubs.
The hyphenation bounds for a particular language can be overridden by creating a file name LANGUAGE_CODE.bounds in the hyphenation-patterns directory. The content of this file must the minimum number of letters before the hyphenation point relative to the beginning and end of the word, separated by a space. You can disable hyphenation all together by uncommenting the corresponding line in config.sh.
Dictionaries in the StarDict and dictd formats can be placed in the dictionaries directory. StarDict dictionaries should be placed as uncompressed folders containing an .ifo file. Plato doesn't support StarDict natively and will therefore convert all the StarDict dictionaries it might find in the dictionaries directory during startup. You can disable this behavior by uncommenting the corresponding line in config.sh.
The four scripts scripts/wifi-{pre,post}-{up,down}.sh can be created with commands to run before or after the WiFi is enabled or disabled, respectively.
Go to the Releases page and download the latest. Unzip to location where Plato is installed (usually .adds/plato/) and overwrite all files. Your settings will be preserved.
Always read the release notes as they contain actual, useful information!