Air Register problem

[moorem]

Hi All. I am having the air ducts in my house professionally cleaned tomorrow afternoon and we have a variety of different air registers in the old house. Some I can lift out, some are nailed to the wood floor, which I can pull out, but some are attached with liquid nails or a similar adhesive. Does anyone have a recommedation on how to remove them without damaging the registers? I don't know why the original owner attached them this way. Here's the style that they are:




Thanks!