how can I down the linode plan?

Downsizing your Linode plan is a great way to reduce invoices. There's another Community Question post that provides steps for what to consider when looking to downsize your plan:

Downgrade Linode to smaller size plan

Important things to know about resizing to a smaller plan is that you'll need to resize your Linode's disk before resizing the plan.

Specs for each plan are listed on our pricing page, which will help you in determining what size plan you can resize down to.

Thanks for answering.

The question I have is
If my disk size is currently 1280GB and the plan I want to downgrade is 640GB
How can I make the plan change?

You can resize a Linodes disk from the Disks/Configs section of your Linode. We have a guide on doing so here, though the guide calls the section Advanced Configurations:

https://www.linode.com/docs/quick-answers/linode-platform/resize-a-linode-disk/

The Advanced Configurations section was recently split into the "Settings" and "Disks/Configs" pages, so once you get to the Disks/Configs page you're in the right place.

From there, click on the three dots symbol on the row for the disk you'd like to resize, then click on "Resize" in the dropdown menu that appears. Your
Linode will need to be powered off to resize a disk.

If there’s anything else I can do for you or any questions I can answer please don’t hesitate to ask.

Best Regards,
Michael J.
Linode Support

So,First I make the change of the disk to 640GB and later, I make the change of plan without the option to resize the disk?

@luisa_lopera - Yep! You need to downsize the disk first in order to resize your Linode's plan.