how do you delete vendors with transactions?

Reason: when we first starting using Adagio we had no way to distinguish between US & CDN vendors. However, shortly after that time, we now use first four letters of vendor name and 01-50 CDN vendor and 51-99 for US vendor.

now, i'd like to delete the old vendors with wrong vendor codes. how do i do that when the system says,

"... not permitted, transactions on file"

Thanks, Gil