Finally managed to clone my 256 SD card to larger 512 SD
The first process is pretty easy following this method:
A guide on migrating a whole partition or drive in SteamOS or Linux in general.
handheld.quest
sudo dd if=/dev/$OLDCARDNAME of=/dev/$NEWCARDNAME status=progress bs=100M
but well once is cloned the issues starts
It only recognizes the old size. And doesn't let you expand the full SD card capacity on KDE Partition Manager.
I found on google it was a common issue for many people
People was saying to use gpart boot ISO. Well I tried but the problem is boot that iso on deck it's not practical. And as you can read on that site seems neither works xD
Trying different things I crashed boot Deck system so I had to use official recovery ISO (lol)
help.steampowered.com
Then I finally found a very simple method I hope be helpful for some people.
If you go to your windows PC, connect your SD and use Disk Management to create a new Partition and once it's created, delete it and go back to your Steam Deck.
KDE Partition Manager recognize the whole SD capacity and lets you resize the cloned one to the maximun size.
In summary, if you have this problem, go to Windows, create a simple partition, delete it, go back to Steam Deck, use KDE Partition Manager, and resize it.
Time to fill it with ROMs and VNs ^^.