window handles

I am trying to replace window handles since we don't have the keys for the current ones. My first problem is figuring out how to remove them, they do not twist or slide and I can't see any screws anywhere. Any ideas? After that it might be hard to fine replacements that work on these sizes, is...

Hi all, please can I get your help in removing these window handles which have no visible screws and no obvious screw covers?