In SSMS/Database/Properties/Filegroups I found my FileGroup, it has 0 under Files column. I pressed Remove button and then OK, but got a message :

Drop failed for FileGroup 'lpad_20090124'. (Microsoft.SqlServer Smo)

Additional information:

Exception occured while executing Transact-SQL stetement or batch.(Microsoft.SqlServer.ConnectionInfo)

The filegroup 'lpad_20090124' cannot be removed because it is not empty. (Microsoft SQL Server, Error: 5042)