Basement leak behind electrical panel
&quot;Can I take the electrical panel off the wall...&quot;

Yes, but removing it requires the feed conductors and circuit conductors to be disconnected. This is a big job and (depending on your local code authority) a licensed electrician may be a requirement. If you are allowed to DIY and you are comfortable working with conduit, breakers, wire connections, etc., make sure you take a bunch of pictures before and during and label everything carefully.
If you are asking &quot;how do I do that&quot;, than I propose you call an electrician.


&quot;Do I need to turn the power off?&quot;

Absolutely. Again, the fact that you are asking makes it clear that to safely complete the project you should call a reputable licensed electrician. It will be worth every penny of the cost, believe me.