Before we start this very simple tutorial, I have to tell you some things:
[*]If your IPB is version 3.4.5, you have to download a theme that is compatible with v3.4.5, or it will look bad, and will have some major bugs, glitches, etc.
[*]Editing the title for some themes is difficult, but nothing that can't be handled. Basically, some these have text for "logos", like the "Uniform" theme, but others, like the default theme, need logos. The simple solution is to make a logo that is plain text, and use the easy logo changer to upload it to your desired theme. Now let's get started, shall we?
[*]Download a theme from a website, making sure you've read the two bullet points above.
[*]Extract it to somewhere easy to find, like your desktop.
[*]When you look through all the directories, you will fall upon one with two files.
[*]This step is very important, when you're importing the theme, you have to import both the image set, and then the actual theme. It is important that you know which of the two files is the image set, and which of the two files is the actual theme. Most of the time, the image set will be named images-themename.xml.gz, or something similar to this.
[*]After you've uploaded both of those files successfully, you still want to make the theme visible for others, in that case, you go to the theme settings, and tick the button that says "make theme visible" or something similar to that. You may also want to remove the (Import) from he name of your theme, it look a whole lot better.
[*]And finally, if you want to make the theme your default theme, while doing the steps above, also tick the "make default theme" button. (Name may not be correct, but it will be clear to you what I mean once you're editing the theme). And you're done! Enjoy your theme.