Yes. So say you have 3 4TB drives. Which would give you 8TB of usable storage.
Replacing one of them with 8TB drive will not give you more storage. But if you buy 3 8TB drives, replace one of the 4TB drives, allow it to rebuild, then do the same for the remaining drives, after the last 8 TB is installed and rebuilt it will automatically expand to 16TB of usable storage.