First line of the first screen shot tells you why ... you have Moodle 2.6.1+ and you cannot upgrade (it's really referring to the database for your moodle) from that version to 3.6.highest without first upgrading to 3.1.highest.
Hope you began with a backup of code and database.
Am guessing you acquired new code and put it in new directory. Used config.php from the 2.6.1+ site in the new code directory. The db for your 2.6.1+ moodle knows it's 2.6.1+ and the code check for upgrades (system requirements) catches and informs.
Afraid you have 'march' your moodle a little ... upgrade it in stages (backing up gains as you go).
2.6.1 to 2.9.highest ... upgrade check the site out, backup, then next hop ....
2.9.highest to 3.1.highest ... upgrade, check the site out, backup, then next hop ... which 3.6.highest.
Am almost certain those willing to work on it for you might require some more info ... for example ... is your site on shared hosting with hostgator or a VPS? Gonna say that if on shared hosting, you need to pursue moving from shared to either managed or un-managed VPS.
'spirit of sharing', Ken