Delete will take time as OPC mentioned above as it has to reference child tables too .
Two approaches are there.
although it is not recommened if you are following strictly the FK concept BUT yes , remove the FK constraints then do the delete from parent + childs tables (CAREFULLY handle the data to avoid orphans records)
Second, take the batch approach for delete operation.
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)