Hi Gino,
Was the work done under contract? If so, was it stated that the job was "Work for hire"? The law stipulates that an artist retains full legal ownership unless otherwise stated. Even if the job has been paid for, in full, and the files were sent to you. As for Logotournament, and the designers here, you don't need to worry about ownership, because we basically sign off ownership to the client in the contract you recieve. However outside of Logotournament, it is a common mistake that most people make, thinking that because they hired and paid for a job, they own it. In essence you only have a license to use the logo. I personally transfer ownership to all my clients, but not everyone does. Some contracts will only allow you to use the logo only in a medium, anything beyond, may have to be renegotiated. Without permission or release (such as a "Work for Hire" contract") from the previous artist, you cannot legally rework the logo, unless you are doing a completely different logo. I know it may not sound fair, but it is the law here in the United States. You may want to talk to your previous designers and have them sign off a waiver relinquishing full rights to you. It may be a pain, but you never know when a business relation might go sour. That is usually when the client first finds out that the logo they have paid for and been using for years, never belonged to them.
Hope this helps. Good luck and all the best.
Night Owl