Erase old Time Machine backup files

I inherited an old external hard drive that I would like to use with Time Machine on a computer. However, the drive was used as a backup with Time Machine on another computer that has since been wiped clean and is no longer available. Unfortunately, the external drive still has the old TM backup files from the old computer. I've found that I cannot simply delete the backup files from the external drive.

How can I delete the TM backup files from the external drive? Will erasing via Disk Utility handles this?