uh, that guide confuses even me who knows the steps >.< not everyone think the same way, so I'll put a different perspective below.
In broad sense, there are two major steps you need to do, which won't take long.
- Change (untie) any AppVM's that use the template, to your new template.
- Then, and only then, can you delete a template once it's untied from any AppVM''s.
It's that easy, pretty straight forward. But be warned not to confuse when to use dnf remove and qvm-remove, more on that below.
On how to do this;
Right click on desktop and open your dom0 Terminal, write in "qvm-ls", drag the window a bit larger so you can better see the table. Any AppVM's still using the old template will show here.
Once you're done moving templates over to your new template, write in dom0 "Qubes-Global-Settings"and check if the old template isn't being listed here, if it is, change it to the new template instead.
Default system templates, which include both does pre-installed or the ones you download with the command you used, can be removed with "sudo dnf remove qubes-template-fedora-23".
It's here very important that you distinguish between dnf remove and qvm-remote, as it can mess up your system. Only use qvm-remove on regular AppVM's or cloned templates (cloned templates, the ones you cloned and copied yourself). Qvm-remove may also be needed on some standalone VM's, but it's a less frequent situation.
In order to remove a default template, such as fedora, debian, whonix, you need to use the dnf remove command, but first, you need to completely untie your old fedora version, as shown above. If you're unsure how to untie them, it's pretty straight forward, just go to each VM's GUI Settings, and change the template in the first tab window, and that's it. You may want to verify if the AppVM works before you delete the old template though.
Qubes is very modular in this sense, it's a smart build. Simply by untying to the templates, and it'll become delete-able.