Disabling File Custom Field.. Quick way to find / remove old files

I've been using a 'FILE' custom field in my EasySocial events to allow people to upload things... I'm now proposing to stop using that and instead use the 'share files' and 'file application' system which from testing ES2 I've realised is much better for what I need.

My question is, because my ES site has run for many many months now, lots of files have been uploaded by people through that 'FILE' custom field for Events... and so is there an easy way for me to find these in my Joomla site file and folder structure.. and would it be safe to delete those files? Thanks!