How can I safely delete older Time Machine backups from my network connected Synology NAS drive

Hi all, I am having major issues with Time Machine and the backups I have made over the past 2 1/2 years.  I am running a mid-2017, 27", 5k retina, core-i5, 3.5, iMac.  iMac 18,3 or A1419.  I am backing up over the network to a Synology DS414J with 2 identical WD 6Tb drives in a RAID 1 setup.  I upgraded from Mojave to Catalina about 3 weeks ago and started to notice that my backups were not completing.  After further investigation after receiving a message that Time Machine completed a verification of my backups and speaking with Apple and Synology, I was told that the Time Machine backups were corrupted and that I would need to click Start New Backup on the error message window to reset my Time Machine backups.  I did so and then a few hours later I received a message that my Synology drive only had about 1Gb left on it and the Start New Backup process failed.  So now I get to the real point of this thread, I need to make room on the Synology drive so that I can run the new backup process over again.  How can I safely delete old time machine backups from the Synology drive?  I have read that you can delete them one at a time when you Enter Time Machine and select a backup and then delete that backup.  I have also read that you can delete backups through the Terminal application using the Time Machine utility tmutil?  I don't want to lose all my backups but I need to free up some space so I can get Time Machine working correctly and showing all my prior backups.  Once I do that, I will add hard drive space to the Synology drive and continue on with my life.  Please advise me how to safely remove old backups from the Synology drive.  My other consideration is I am not sure how much space I will need to free up in order to run the Start New Backup process?  I have tried to explain the situation thoroughly but if you need more information just please ask me.  Thank you very much!