depends what sort and then the condition, one piece or three-piece?
Some are fixed to the glass, double sided tape on either the attaching points or the retainers and will need scraping off. Others have hinged areas for glass cleaning and use a key. These are also often damaged, have missing parts or missing keys and then also get fixed permanently to glass. And then there are some that slip under the window trim for fixing points so need to also remove that for best access to remove cleanly.
I also had a used unit that was a mixture of them all, was missing parts that made it lift up, had new parts from back yard job to secure missing parts, and then had riveted extension strips to slip behind trim as a fix. They are 40 years old, a long time for some people to not decide to remove for looks or to clean and keep intact.
