Hi Raj,
ECC delta queue are not mandatory to clean it.
But safe side you can load the delta records from psa to all connected targets.
you need to stop your present loads and reschedule them.
Please refer oss notes :
1403832
1636053
1000009
Even there are some more docs on Google. please search them by using search term as "bw 7.3 upgrade check list".
Thanks