You asked for Roman, so I did not answer your question. Very sorry to keep you waiting.
You have child theme activated, so you cannot delete the parent theme, in this case, the parent theme is Alora Theme.
This is how WordPress works, because child theme needs the parent theme’s template to work, so logically you cannot delete parent theme while child theme is activated.
If you only have css added to your style.css of alora-child, then you should have no problem.
But if you have other templates in your alora-child that is used to overwrite the Alora Theme, then you should try out on your computer first. This is because codes in version 2.7 may have been very different from 2.5. I am not the person developing the Alora Theme, so I do not know what has been updated.
If you have no template overriding on alora-child, then you can keep a copy of Alora 2.5 on your computer and proceed to update your server with Alora 2.7
If you are not sure, then you should setup a “single” WordPress installation on your computer and install your alora-child and Alora version 2.7 for compatibility check before updating your server.