Image resize

i want a plugin or something to do next thing:

if you see here ( https://www.1×2-sports.com/galerie-foto-miss-tuning-2012-iata-castigatoarea-si-finalistele/ ), i have 10 gallery pictures. when i click on a photo from that gallery, i don’t want to display that image in a new tab.i wanna make it full size right there in the post.
what plugin i need to install?

thanks