How can I exchange Discourse icons for others?

I want to exchange for android icons Or by light icons

Are you talking about icons or emojis?

If you are talking about emojis, look for the “emoji set” setting:

About the icons, I think the standard Discourse icons are too rustic, I want to change them to lighter icons or more similar to those on iOS or Android

like this

Material Symbols and Icons - Google Fonts

You can’t just swap from font-awesome to another set, you’ll need to load your new icons and replace the current ones one by one.