no other option than brute force attack. Attack may take long time depending on strength of the password. If password is listed in dictionary u can break it in short time if not may take many days - years to break it. If u can remember the length of the password, upper-case/ lower-case, .... u may able to reduce the attack time. Othervise sorry.com
Also you can break it with a super computer with a reasonable time.
RAR uses 128 AES encryption that is not currently breakable without a brute force attack.