After finishing a document with images anchored to a page, If i edit the text, all the text below is relocated. How do i avoid this?
I think your idea of how it should work is just wrong.
Text cannot be anchored to a page. It is so called continuous text. The more you write and a page is full, the further written text moves to the next page.
If you want to add an image to a paragraph, you can anchor the image to the paragraph so that the image stays on the paragraph.
I hope I could express myself understandably.
@Astur,
Plain text is entered first with basic formatting such as bold, italic, underline, …
I hope you mean format with styles.
@Astur It wasn’t a criticism.
Yes, this can also happen if you use direct formatting and formatting with styles.
Well, at least you didn’t work with stone tablets. (it’s a joke). 
Your mistake is to anchor your images To page. This anchor mode associate the image to a physical page. Text flow will occur around this image.
Suppose page 7 was current when you anchored your image. It will stay on page 7, whatever may happen to your text. If you ever remove text so that it needs only 4 pages, your image is still on page 7. This results in fake blank pages 5 & 6 you can’t delete!
This rather surprises users unfamiliar with the definition of anchor modes.
What you need in fact is to anchor your image to some paragraph (perhaps the description of the image) so that it moves with this paragraph, always remaining in its vicinity (at least the same page). To paragraph does not prevent you from positioning the image anywhere in the page. An image is associated with a frame. Right-click on it and Properties. Go to the Type tab and tune the Position parameters. You have many possible reference points: paragraph, margin, page, …
The best strategy in case you have similar images to be positioned identically is to define a user frame style holding all your preferred parameters. All you must do then is to assign this frame style to the image with a double-click on its name.
Frame styles are described in the Writer Guide.
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