In theory, that's how RAID5 works. In practice, not all devices/manufacturer offer that basic functionality. Check with your RAID device manufacturer to ensure this is supported by your device. Also verify if there is a space limitation with your device.
If it is, the process is to replace one 1.5TB disk with a new 3TB disk, then rebuild the RAID array. Repeat this process until all 4 disks have been replace (ensure that the rebuild is completed before replacing another disk or you will loose your data). Once all the disks have been swapped with 3TB, use the RAID device utility to grow or expand to RAID array to the new size.