1 / You are right, surely I have read it in posts that I have found in google and with which I have learned to make the change!
2 / My language pack is Spanish!

Thanks for your reply, I will update now!

Hi Fotis, we upgrade but the problem persist when we selected a image from the server!

"Notice
The image was not uploaded. Please ensure that you used a valid image file and that file uploads are properly configured on your server."

Now we have a new error when click on "ExistingImage" (this link https://......../administrator/index.php?option=com_k2&view=media&type=image&tmpl=component&fieldID=existingImageValue#elf_l1_Q29udGVuaWRvcy8tQmFja3Vw)

Refused to apply style from 'https://.../administrator/css/theme.css' because its MIME type ('text/html') is not a supported stylesheet MIME type, and strict MIME checking is enabled.