Upgrading Electricity from 60 to 100 Amperes

Can somebody give me a rough idea of how much it would cost to upgrade the electrictiy delievered to a unit from 60 amperes to 100? Our building has three wire service, 120/240 voltage with 200 amperes available in a 4 unit building. However, it is currently controlled by 150 ampere cartidges in the main box. Recommendations for the job would also be appreciated. Thanks!