I know from the CBSSPORTS site that we use in my other league that you have to set it up to a maximum number of roster spots. We have a draft of 20 players and then have to reduce your roster to 17 by the end of October. Afterwards you cannot lower the limits because it will affect the stats in prior weeks. I think this is the case here as well, but not being the commissioner, and not being familiar with ESPN, I do not know what changes you can make on this site.