The upgrade from 4.1(5) to 5.0(1) is done via FTP. It looks like you have a connectivity or log in problem between your sensor and the FTP server. Make sure your account info and filename exists on the FTP server. The command for upgrading is very straighforward:
conf t
upgrade ftp://@/IPS-K9-maj-5.0-1c-S149.rpm.pkg