Both menu items are near the bottom of the "Render" menu. It's actually nice to have "Keep" checked because loading the textures is the first step in a render and can take a while. Be keeping the previously loaded texture files in memory, poser can skip that step when you render the same scene over and over, messing with lights and what not. You want to turn it off in when, as you are doing, you are changing the file contents between renders.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)