Why would you want to do that? If you had created all the software by yourself, I would say yes, do it! But in this case, I assume you did downlaod and install it, maybe some tweaks here and there. I am sure that there are put lots of hours / days/ weeks in this sotware by the team of oxwall. It won't be fair to delete the logo. I am not sure if you are even allowed to do that.
EDIT: Oxwall is licensed under CPAL 1.0. Please, read short terms of this license here <-- A quote from Addenster