You need to be looking at folders on the server. Look in moodle/lib/editor - the tinymce folder should be in there. Try copying over that same folder from your original moodle installation (if you have it). If not, you then need to go to the Moodle downloads and download a 2.6 version that is closest to what you are running and then copy the folder over (just the tinymce folder).
An upgrade is not a button click. You need to download the new moodle code, manually copy over any plugins and the config.php file and any themes that you use and then rename the old folder to something different and rename the new folder to moodle or whatever your folder is called now (sometimes public_html e.g.). You need to read the instructions here - https://docs.moodle.org/28/en/Upgrading
Also, there was a big theme change in 2.7 (adding responsiveness) but it might affect your theme.