[Plugin: NextGEN Gallery 1.9.10] – Doesn't work! Help please!

Hi there! I recently had updated my WP site > http://www.arqueologiadigital.com.ar to 3.5 version, but since that I realised that when I want to put the main image for a post, WP only allows me to upload a new image, so I couldn’t use no one from the gallery.

I have a lot of images uploaded to NextGEN! Please help!

Thanks in advance and merry xmas!