How to maintain the position of the site if we completely redesign it?

Question

Search Engine Optimization

There is an old site mahatma.com.ua with a certain position in the search engine (an SEO specialist once worked with it, but no one did it for a couple of years)
We want to completely replace the site (different design, content, CMS)
Question: Is it possible to partially or completely save site positions? What needs to be done for this?

Answer 1

If you completely replace the site including the content, then naturally there will be no positions. The only trust will remain, which will positively affect the growth of new keywords

Answer 2

If you change everything, the positions will sag.
If you do it carefully and little by little, you can save it.