we can select the volume which we required to delete/terminate, if the volume attached to a running instance then select Volume => actions => detach volume => delete volume,
Also if the the option delete on termination is enabled for a instance then this volume will be deleted once the instance terminated
we can expand the EBS volume by selecting the volume => actions => modify volume => increase the volume => modify this way we can expand the volume.
No, you can't reduce the EBS volume, We can create a small volume and we can migrate the data to that volume.