No Problem at all.

Just make a copy of all of the e-credits so that you know the numbers. Login to your delta account and when you have started the booking process make sure that you use the option to pay with e-credits.
I believe you are only allowed to uses five e-credits per booking. If the amount of your e-credits is less than quoted price of the booking you will receive another e.credit (depends whose e-credit had a balance. if it is more you can pay the difference with your credit card.
It`s very simple to do . I have done it numerous times as I have had lots of e-credits because of the flights that I have had to cancel. As I was sure that i would be traveling I opted to receive e-credits