Upgrading from 2.10.x?
Okay, Back up your database using your cPanel/Plesk/server control Panel/phpMyAdmin etc.
Load your config.php file into a text editor.
Rename your version 2 phpList directory to lists2 (for example)
Download the latest version 3.x.x
Unzip it to your computer. (You should be able to do this easily with Windows XP/7 8 & 10 should also work). If you are unable to unzip the file, download WinZip, you should be able to get a 20-30 day free trial. Winrar has a 40 day trial and does work with ZIP and GZ files.
Once unzipped, upload from your computer to your server, the entire contents of the lists directory to your lists directory on your web space, or upload lists directory to your root directory. Whichever is easiest for you.
DO NOT OVERWRITE your version 2 directory! Version 3 is very different, you need to start afresh.
Now, look at the version 3 config/config.php file and amend the settings to match your current config.php file. Mainly put your database settings in (use your backed up database here), your mail settings, and your $pageroot setting (you do NOT need the admin url settings).
This should get you started with the updating of your phpList to version 3.
If everything goes badly wrong, then you still have the backup lists2 directory which uses your old version 2 database, which you can go back to by deleting the new lists directory and renaming lists2 back to lists.
Hope that helps