Changing Templates? Please reply

I downloaded subBlack template and installed it in my forum.
I don’t want the whole black and gold look, I want a black and blue look and when I was trying to change the font colour it just changed the font colour in the admin panel but not on the forum.
Is it possible to change templates you’ve downloaded or do I have to make my own template?
I would also appreciate if you could tell me where & how I put a banner and background.
Please help me, I want to open my forum ASAP.

This is phpbb, right?

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click the link and you’ll see what a phpbb forum looks like.