How to speed up the delete process on SQL server

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SQL

I have two tables, having parent-child relation. Each table contains around 14 lakh records. I want to delete data from the parent table along with the associated records in child table. The count of records to be deleted is around 4 lakh.
Directly firing a DELETE query in SQL freezes the database server. As the database is being used, I need a solution which will not cause the database to freeze. There are no indexes on both tables, but there are foreign keys in 4 other tables which reference a column of the child table (mentioned above).

Is there something which can speed up the delete process without freezing the database?

What I have tried:

I tried running a delete query on parent table which cascade delete the records from child table, but this freezes the database server. Currently i am using a console application(created using c#) which gets the list of folders and deleting them one by one.