Dear Ajay,
I am not sure whether we are able to increase size of a pipe. Maybe you can consult netbackup.
However we can increase parallel from 2 parallel which is currently you are using. You can increase parameter MaxBackupMedia and then you can define more parallel when creating backup template.
Please note MaxBackupMedia only takes effect after restarting database. You may need to try to give 4 parallel, because it is not more parallel more better. You have to find a suitable parallel for your
landscape.
Best regards,
James