Auto Archive Creation

Another question- let's say my archives are set to automatically create.  How can I change the size?  I believe it was set to autocreate the size as the current (at that time) archive size.  The problem here is that as the system size has grown, the duration of the archives has shrunk- down to about 2 days.  I would like to change this to have larger durations, and thus larger archive sizes.  What is the best way to do this?  Disable it, create a new larger archive, and then shift- then enable again?

Thanks,

Scott