[the following assumes you’re using DAZ|Studio… if you’re using Poser, please ignore this]
You can also turn off “Limits”, if that is what the OP is asking…
... on the Parameters tab, at the far right there is an icon which looks like a small triangle and a bunch of horizontal lines. If you click that, you’ll find the option to turn off Limits Off (Rotation) (which will allow you to bend legs past the 100degree mark). Or, you can click on the little “cogwheel” to the right of each parameter and select “Parameter Settings…”, which will allow you to turn off the limits for just that parameter. Either way, you’ll be able to bend the legs to anything you desire (even physically impossible angles).
Note that the body starts to look a bit “bleaugh” when you go too far past the limits, so the product Ariana mentions above will help to smooth things back out again.
ETA: if the pose you have in mind is something similar, then this set by Meipe will probably give you the best looking figure (as each pose has been specially “hand-smoothed” to look right - the downside is that the smoothing is ONLY for that particular pose, and it doesn’t look so good when you start to move the limbs where the smoothing has occurred) :