Awning window trouble opening

I have 4 awning windows that have latches that engage on the sides as the window is completely shut. The trouble is that these latches are beginning to stick and continue to hold the window from opening when attempting to crank it open.
Has anyone else had this problem? What parts do I need to tighten/replace in order to get these latches to unlock as the window is cranked open? I have also tried to get a basic schematic for awning windows without success.
Thanks in advance for any info...
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