$ sudo apt install libguestfs-tools

$ qemu-img convert -O qcow2 /home/gean/kvm/images/EVE.qcow2 eve-small.qcow2

$ qemu-img info eve-small.qcow2 
image: eve-small.qcow2
file format: qcow2
virtual size: 64 GiB (68719476736 bytes)
disk size: 35.3 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
    extended l2: false

$ sudo virt-sparsify --in-place eve-small.qcow2

$ qemu-img info eve-small.qcow2 
image: eve-small.qcow2
file format: qcow2
virtual size: 64 GiB (68719476736 bytes)
disk size: 12 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
    extended l2: false

$ qemu-img convert -O qcow2 -c eve-small.qcow2 eve.qcow2 

$ qemu-img info eve.qcow2 
image: eve.qcow2
file format: qcow2
virtual size: 64 GiB (68719476736 bytes)
disk size: 5.81 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
    extended l2: false

Referências

1. How to shrink OpenStack qcow2 image using qemu-img
2. How to resize a qcow2 disk image on Linux
3. 21.14. virt-sparsify: Reclaiming Empty Disk Space