You might see around some different ways to reset admin password.
For example by coding, by using a Sitecore Module and etc.
This one is on database level and it works really well.
Complete information on Sitecore.StackExchange but the SQL query is also below.
Run this SQL on your CORE database and you will reset admin password to ‘b’.
I hope that helps.
UPDATE [aspnet_Membership] SET [Password]='qOvF8m8F2IcWMvfOBjJYHmfLABc=', [PasswordSalt]='OM5gu45RQuJ76itRvkSPFw==', [IsApproved] = '1', [IsLockedOut] = '0' WHERE UserId IN ( SELECT UserId FROM dbo.aspnet_Users WHERE UserName = 'sitecore\Admin' )