If the downloader isn't working, try downloading the latest (build 250) separately from here and installing: https://www.vegascreativesoftware.info/us/forum/faq-where-can-i-download-vegas-pro-and-other-vegas-software--104782/

Older versions should be removable from add or remove programs. If not try an uninstaller to wipe out a corrupted install first. (Revo uninstaller?)