How to open a components' schematic symbol for editing quickly in Altium
Double click the component, note the library name (you likely already have it open) , copy the Design item ID (Ctrl-C), switch to SCH LIB view for the library and paste (Ctrl-V) into the box at the top.
I don't know of a faster way.
Keep in mind that you should not be casually editing library components regularly as the edit may affect other PCBs if they are updated from that library. You may want to copy the existing component into a new Design item ID or a new library.