Use 7-zip or WinRar to extract the contents.
With the files right next to each other in the same folder using the same name but differing only in the part number:
1. Right click on the first archive, the one with "part1.rar" at the end
2. Hover over the "7-Zip" option in the context menu
3. Select "Test archive"
- If it says there are no errors, then you are golden and can move on to the next step.
- If it cannot find the second part on its own because it says it is missing, then make sure they have exactly the same name and differ only in the part1.rar and part2.rar name at the end.
- If it says there were errors, then at least one of the files is corrupt and you will need to redownload the corrupt part. I am not sure if 7-Zip or WinRar will say which one is corrupt.
4. If there were no errors, then close the box that says there were no errors -> "OK"
5. Right click on the first archive
6. Hover over the 7-Zip option in the context menu
7. Extract to "Folder Name\"...
- "Folder Name" will be the name of the archive in step 1.
8. Extracting should work now, so just wait for it to complete.
9. Look for the files under the "Folder Name\"
- "Folder Name" will be the name of the archive in step 1.