That rollback plugin is one of the options listed. If you don’t want to mess with FTP then I’d try that.
I you download from the other URL then you’ll need to upload manually. Basically you need to connect with FTP and delete the acf folder from your plugins and then upload the older version.
Rolling back to version 4.0
If you’d like to go back to an earlier version of ACF, we recommend using this rollback plugin, which is available from the WordPress repository. Once installed, use the Dashboard > Plugins page to Rollback the ACF plugin.
Alternatively, you can rollback manually by downloading an older version of ACF and uploading it to your server via your favourite FTP application. Replacing the ACF plugin folder will not affect your data in any way and is a completely safe way to rollback
