How can I safely shrink my Windows partitions and expand Ubuntu?

The exact steps depend on the current partition order. If the unallocated space is separated from Ubuntu by another partition, GParted may need to move that partition before Ubuntu can grow. Take a screenshot of the disk layout first and make a full backup; a power failure or interrupted move can corrupt a partition. If the space cannot be made adjacent, creating a separate Linux data partition may be safer than moving a large existing installation.

You can use a third-party Windows partition tool, but it is usually unnecessary. Disk Management is the safer first choice for shrinking the Windows volume, while GParted from a live USB is the appropriate tool for resizing or moving the Ubuntu partition. Do not delete the NTFS partitions unless you are certain you no longer need Windows or the shared files.

Boot an Ubuntu live USB and open GParted. The installed Ubuntu partition should not be mounted while you move or resize it, which is why a live environment is recommended. From there, shrink or move the NTFS partitions as needed, then expand the ext4 partition into the adjacent unallocated space. Moving the beginning of an ext4 partition can take a long time, so keep the computer powered reliably and do not interrupt the operation.

Back up anything important first. Use Windows' built-in Disk Management to shrink the Windows partitions, since Windows knows how to safely handle its own NTFS system volume. Disable Fast Startup and fully shut Windows down afterward. This creates unallocated space, but it can only be added directly to the Ubuntu partition if that space is next to it in the partition layout.