If you wish to remove the dataguard/standby setup from primary database i.e to make the primary database as standalone database without any standby database, then follow below steps.

1.Put primary database on maximum performance mode:

2. Remove below parameters from spfile of primary database:

FAL_SERVER
FAL_CLIENT
LOG_ARCHIVE_CONFIG
DB_FILE_NAME_CONVERT
LOG_FILE_NAME_CONVERT
LOG_ARCHIVE_DEST_n – pointing to standby database like _2 or _3
LOG_ARCHIVE_DEST_STATE_n 
STANDBY_ARCHIVE_DEST
STANDBY_FILE_MANAGEMENT

3. Drop all standby log files from primary:

4. Restart the database to reflect the parameters

Now the standby database is completely separated from primary.
If you want to use the standby database as a standalone database, then follow below steps on standby

You can change dbid using NID utility( as dbid would be same as primary)