I assume you have an encrypted drive and don't have its password? If you don't have a recovery password then you will lose everything on that drive. However, if you have simply forgotten your Admin account's login password:
Forgot Your Account Password
For Lion or later
Reset a Mac OS X 10.7 Lion Password
OS X Mountain Lion- Reset a login password,
OS X Mavericks- Solve password problems,
OS X Yosemite- Reset a login password.
macOS Sierra-Reset a login password.
Change or reset the password of a macOS user account - Apple Support.