Hi Santana,
Unfortuantely we dont support changing the field sizes on any out-of-the-box fields. This is something that would be an enhancement which you can post here to the community as an "idea". The reason we do not support changing the size is because if you did an upgrade or migration, or sometimes even patches, new files are delivered which may revert it back, and then you may end up with errors or truncated data related to that field (most likely notification logs could go corrupt on you in this case specifically).
Thanks,
Jon I.