Outlook 2G PST File Size

An outlook account is created and saved as *.pst file which has a limit size of 2GB. That is fine for most but not the contract/financial people here. A couple of employees have locked themselves out of their mailboxes because they met or exceededthat limit. I need to know how to open this file and break it up so they can use it again? We’ve had numerous programmers working on this with no success to date.