These random V2 JSON files always make things complex. We apologize in advance.
You need to convert it to the standard V3 (‘Keystore / UTC’) file. The easiest way is using geth.
Download the appropriate version of the geth based on your operating system.
Once you download it, extract the zip. Also copy your V2 JSON file into the same folder.
There are really explicit instructions you can read for PC and Mac users.
Now you have to open a command line window and type in the following command:
geth account import nameofyourwalletfile
This will import your file into geth and convert it to the latest (V3) keystore file.
Now you need to go find it in one of the following locations:
Copy that file, and select it on MEW, and you’re good to go!
Moving forward, use this file. Keep a backup of it (and the old file, just in case).