How do I edit part SchLib file from SchDoc file in Altium?
I assume what you mean is you have a schematic which contains components wired together.  One of those components needs to be modified for some reason, but there's no easy way to edit the component in the library itself without going to find it.

Firstly, you should really have your libraries installed in Altium. On the right is a button which brings up the libraries. Find the component in there and edit it.

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This will take you straight to the schematic library with the chosen component open and ready to be edited. No messing around in Explorer. 



Alternatively, you can edit some features of the component directly within the schematic; pins names/numbers, description, footprint, etc.  The problem with doing this however is that those changes will be lost if you ever update the component from the libraries.

Double click on the component to bring up its dialog box. There you can edit a bunch of things.  In the bottom left is the 'Edit Pins' button, which lets you edit most of the pins' properties.