RAR files are compressed data files, similar to ZIP files. When large files are compressed into RAR files, they are often split into multiple files to save space. To distinguish between the multiple files, the RAR files are given a number. It is not uncommon when opening a file or document compressed with RAR to have filename0.rar, filename1.rar, filename2.rar, and so on. Merge the files by extracting with WinRAR.
Download WinRAR from the RAR Lab website (see Resources).
Double-click on the downloaded file to open the WinRAR installation window. Press "Install."
Select "RAR" in the Associate WinRAR With menu.
Click "OK" and choose "Done" to complete the installation.
Place all of your RAR files into one folder.
Double-click on the RAR file with the smallest number. In most cases this will be filename0.rar or filename1.rar. All of the RAR files will merge in the extraction into a single file.
Another option is to right-click the RAR file and choose either "Extract Here," which will extract the file to the folder containing the RARs or "Extract to (filename)," which will extract the merged file to a separate folder inside the folder containing the RARs.