How to remove the Forum Spark logo from my forum?

If you're building your own theme:
It may be more convenient to simply remove the header and build your own. To do this, in your active theme's layout (Admin CP -> Themes -> Your active theme -> Edit Layout), you can remove the entire header by removing:

<!-- HEADER -->

Then, you can build a custom header there. Since you downloaded my theme, you can check that theme's layout code for an example (but, of course, you can build it any way you like). In that case, you can upload the logo to your forum (Admin CP -> ForumSpark -> File Manager) and simply add it in your theme layout as an HTML img.

This is what you will end up with upon removing the header:

Also: if you are looking to create new elements regardless of the selected theme, you can also use the board templates (Admin CP -> Themes -> Board Templates). To see where elements would appear, you can simply enter some text and see where everything pops up.

If you wish to use the default theme with your own logo:
Alternatively, if you are just looking to replace the logo instead of building your own header section, go to Admin CP -> Themes -> Your active theme -> Edit Images and simply replace the logo svg file with your own.

Hope this helps.