Use dedicated software like MMC Reader (e.g., Simatic S7 MMC Toolbox) or the commercial S7 MMC Password Recovery tools.

The Siemens S7-300 is a legend—reliable, rugged, but unforgiving with forgotten passwords. With the right tools and a careful hand, you can regain control of your machine. Remember: with great unlocking power comes great responsibility. Secure your backups better next time.

If your backup is named S7_300_Project.rar and WinRAR asks for a password, you cannot simply "remove" it without brute force or known attacks.