how do i load an older autosave from the memory cache

Just click on the little disc icon in the upper right corner.

Then you'll get a list of all your saves you have in game (including the autosave) and can load that.

If it's one you have in a different place then your doc folder, then you need to copy the file to this folder documents\electronicarts\thesims4\saves first and load the game then. If it's an autosave slot, rename it to a different number than 1.

If it's one with .verX at the end, just rename the one without verX and then remove the verX from the one you want to have in your game again