Will the site fall in Yandex search when changing the template?

Question

Search Engine Optimization

Good afternoon. I don't understand SEO, please help me.
There is a site on WP, for many queries it is in the top of Yandex (in Google, few pages broke into the top - but it doesn’t matter). The site has a very bad template, if culturally speaking (in fact, things are even worse))). You need to change it for anyone, so the question is, when changing the template and other related work on the site, how will this affect the search results? The fact is that the whole structure of the site will change, and I understand that the links too. I would be very grateful for clarifications.

Answer 1

To save positions, you need to:
1- save the entire possible url structure
2- save all possible title, h1, description
3- make 301 redirects to the new page for all pages that have changed url
4- make 301 redirects from all deleted pages (if any) to the maximum a similar page in the new structure
5- keep the design of the content of the pages to the maximum, especially those that are now in the top
6- check the availability of landing pages for each request for which you want the site to be in the top

Answer 2

The fact is that the entire structure of the site will change, and I understand that the links too.

This is the only thing that will affect the site's link positions if you keep all the META tags in the new template from the previous one in the HEAD section.
You will need to "glue" old and new links through a 301 redirect and / or canonical.