Follow the below procedure.....

Step 1: Primary server i run below queries.

Note: here MyDB is your database name.

1)delete from msdb.dbo.log_shipping_primaries where primary_database_name = 'MyDB'

2)delete from msdb.dbo.log_shipping_monitor_primary where primary_database= 'MyDB'

3)delete from msdb.dbo.log_shipping_primary_databases where primary_database= 'MyDB'

4)delete from msdb.dbo.log_shipping_primary_secondaries where secondary_database= 'MyDB'

Step 2: Secondary server i run below queries.

1)delete from msdb.dbo.log_shipping_secondary where primary_database='MyDB';

2)delete from msdb.dbo.log_shipping_monitor_secondary where primary_database='MyDB';

3)delete from msdb.dbo.log_shipping_secondary_databases where secondary_database='MyDB';