A VPS disk upgrade increases the virtual disk capacity. It does not automatically extend the guest partition or filesystem. Make a recoverable off-server backup and schedule maintenance before changing storage.
This worked procedure covers a plain ext4 root filesystem on the last partition of a single disk, with contiguous free space immediately after it. It does not cover LVM, encryption, RAID, XFS, a full-disk filesystem or a partition followed by swap/EFI/recovery partitions. Stop if your layout differs; do not delete another partition to force it to fit.
Inspect the existing layout
Activate the upgrade using the power-cycle guide and keep the console open. Inspect the disk from Linux:
Confirm the virtual disk is larger than the root partition and identify the actual disk and partition. If the disk still shows its old size, resolve upgrade activation before altering partitions.
Expand a matching ext4 layout
On Debian or Ubuntu, growpart is supplied by cloud-guest-utils. Review installation before proceeding:
The following example is only for /dev/vda1 on /dev/vda. Substitute your verified values. First inspect the proposed partition change without applying it:
Proceed only if the output extends the intended partition into free space and leaves its start unchanged:
resize2fs is for ext filesystems, not XFS. If the kernel cannot reread the partition table, stop and arrange a clean reboot before continuing; do not force repeated writes.
Verify
Check the expected filesystem capacity and application health. For another layout, obtain a procedure specific to the filesystem and volume manager. If rescue media is required, mount it through the ISO guide, avoid formatting existing data, and eject the ISO before booting from disk again. 
