[Sirtel]

There are several ways.

One is to download the book from the Kobo website (My Account -> My Books). If it has no DRM, you'll get an epub file and there's no need to remove anything. If it has DRM, you'll get a file with the extension .acsm; this must either be opened in Adobe Digital Editions, which will download the actual epub (and you can then get that epub from My Digital Editions folder in Documents), or you can install the deACSM plugin and register it with your Adobe account, then you can add the .acsm file directly to Calibre and the plugin will fetch it as epub.

Other ways are copying the books from your Kobo device or from the Kobo Desktop app. For this you need the obok plugin from the deDRM folder. As I've never used those methods, I'm not really sure how they work.