First of all, please note that a correct submission should have exactly 7555 predictions (please read carefully the description of the submission format: https://knowledgepit.fedcsis.org/mod/page/view.php?id=1012).
There is no need for deleting submissions since there is no limitation to the number of submissions by a single participant. You can submit many times but you should select your final submission manually before the end of the competition. If you do not do it, your final submission will be chosen automatically as the one with the highest preliminary score.
I hope that this explanation helps :-)