Hi
Thankyou for using the forum, Do you have a USB drive you could use for a backup of the 128GB drive ?
If so then you could backup the drive then restore after installing the the replacement 500GB.
A program to consider is the free version of Todo backup. Using the System Backup option allows a full copy of the source drive and a restore to the new drive with a resize to use the full 500 GB.
to use the program download the free version, make recovery media then boot the computer from the recovery media, Select System backup. When the backup is finished. follow the guide on the Dell website to swap out the drive. Boot from the recovery media and then restore the backup.
If you haven't already brought the 500gb drive it would be a good idea to buy a drive with a heatsink or get a heat sink for your drive.
the M2 PCIe SSD run hot without a heatsink.
If you don't have a USB hard drive available then a PCIE card to M2 could be an option.
Something like this
ZoeRax NVME Pro Adapter M.2 NVME Pro SSD to PCIe 4.0
You could then have both drives in the computer and skip the backup to USB step.
Instead of TODO backup you could use the free software available from the new drives site.