Hi everyone and sorry for this stupid question and for my bad english
I use RouterOS from some years ago but, as per every upgrade, i'm a little bit scared

I upgraded my RB1100 board from 5.22 to 5.26, using the Auto Upgrade function and everything is working well.
Now i'm interested upgrading my 5.26 to 6.13, but the Auto Upgrade button don't shows me any available package.

Can i upgrade? How?

system licence print is telling me Thank you

You should be able to upgrade "manually".

i.e.
1. Download the "All packages" archive.
2. Extract it.
3. Upload all of the files that were extracted to the router's "/file" menu.
4. Reboot the router.

It will upgrade upon the next boot.

(See this wiki page for details)