Free up unused space on external SSD using Big Sur?

[DLIT17]

Hi - I've been migrating my large older iMac onto a smaller Mac mini, and purchased a couple of small external SSD drives. I've had a couple of crashes during the migration but the drives seem now to be working fine. The problem is that one has filled up far too quickly (for example, it shows that one folder has something like 850GM in it, even though all of the items together in it are about 130GB). So I'm assuming somewhere in the migration process, additional space was used but not then made available. The online guides seem to say use "erase" on disk utility, but on Big Sur, my only option appears to be to erase the entire disk, not just to clear unused space. Is there a way to identify unused space and free it up on an external SSD? Thank you!

 

[HDFan]

There are various utilities that allow you to see how space is used on a disk, such as Daisydisk. Some allow you to delete items in the application itself.

If you are using DaisyDisk, when you initiate the scan do it as an administrator (right click).

 

[DLIT17]

There are various utilities that allow you to see how space is used on a disk, such as Daisydisk. Some allow you to delete items in the application itself.

If you are using DaisyDisk, when you initiate the scan do it as an administrator (right click).

Thank you very much for the speedy and helpful response!