Trying to decrypt this post, it seems like you wish to delete the file named zlinux, rename zlinux.old to zlinux, but you are only in a file manager (datei manager?) and not in the directory where the file is.
Usually a file manager will allow you to remove and rename files.
What distribution are you using?
What file manager are you using? (For example, dolphin, thunar, nemo, pcmanfm, nautilus ...?)
In any case to solve your problem as I understand it, you need to find the file zlinux, and then remove it and rename zlinux.old. That's easy in a terminal.
Open a terminal. There's probably an icon on your desktop showing a terminal, so you can click it.
I don't know where the file zlinux is on your filesystem, so you can search the whole filesystem with this command as user or root:
find / -name zlinux 2>/dev/null
Wait for the command to finish. It will take a little time because it's looking through the whole installation.
The "2>/dev/null" just stops a lot of output which find cannot access.
If you know the file is just in your home directory, then you can run this command instead:
find /home/<username> -name zlinux
where you replace <username> with your user name.
Let's say the files are found here: /home/<username>/zlinux, and here: /home/<username>/zlinux.old.
To remove one and rename the other run:
mv /home/<username>/zlinux.old /home/<username>/zlinux
If by chance the file zlinux is in the partitions where you need root access, you must run the same commands above as root. There are other ways of doing it, but the above will work.
It occurs to me that the zlinux might be a vmlinuz file, which is a kernel. It's best to deal with removing these files with a package manager.