For most WordPress users, modifying your usual default theme these days has become easier with the advent of widgets. Before, people had to know at least basic html to modify the layouts that these themes had. Also, for advertisers, to be able to place banner ads, sinking in to the usual page template as the sidebar needs to be opened via the theme editor.
The problem here is once you fail to trace what you were able to tinker around, chances are you may mess up the whole WordPress theme, forcing you to use another them to save the exposure of your blog.
Today, all you have to do is use the text widget, paste the code there and choose the sidebar where you want it to be placed. It is that easy. Save it and you and check out if the placement is good. It doesn’t get simpler than that.
So whenever you are prompted to upgrade, check out the new version and what it carries. The newer version support widget capability and thus eliminates the need to download further plug-ins for WordPress that make your site entirely harder to manage.
There are daily widgets that you can use as well and they come in the form of plug-ins via the WordPress developers. But a word of caution. Try not to overdo it. Too many widgets not only make it harder to manage but make it complicated for you to stabilize as far as ideal design is concerned.