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In Site Admin | Preferences | General Settings
There should be a fields where you can enter your Site Name and Slogan.
As for your other question, I'm not exactly sure. If you send a link, I can make a better guess.
I suspect you can customize it by figuring out which module is generating the text, and then editing the template for that module. Sorry I'm not being more specific... perhaps someone else can shed additional light on that for you.
I hope that helps.