As sunami88 says, it may be easiest to redownload them to your PC. First install desktop Adobe Digital Editions and then downloads the ebooks in a web browser. Usually, this automatically opens ADE which downloads the actual ePub for you. Under Windows, the ebooks end up in My Documents\My Digital Editions. If you originally used desktop ADE to get the ebooks to your Kobo, the epubs should already be in this directory from the first download.
If you get a naked .acsm file from your browser, open it with ADE (e.g. right click on it and select ADE) and you should get the actual ePub. The .acsm file is a "permission slip" to download the actual epub from Adobe's servers.