1.9.6 is very end of life I don't even have a test server running it anymore. You should really consider upgrading as there are a number of security issues with older versions.
I think that you can edit the database directly to increase the size of the field. The length (field size) in that version is likely limited by the field size/type at the database level. I'm not to sure where that would be, but if you can tell me what page you have the field on I might be able to guess.