Can i turn a light switch into an outlet?
First, is this legal?. NEC requires switches in certain specific locations.   What's more, some cities also require switches in cetain locations.   Not least, that's so emergency responders can get the lights on, so an EMT can treat you, or a cop doesn't shoot your son because she can't see that's a computer mouse.  Run this by your electrical inspector. 

Ok then.  

Turn off the circuit.  Look inside the lamp box. Is there 3-wire  (black white red) cable there?   

We know there is 3-wire cable inside the switches, because that's how those switches work.

If this is on conduit we'll have to revisit.  But assuming this is done in cable... The 3 colors are always black white red.   Right mow the colors mean gibberish.  We will give the colors meaning.  And that means every place those 3-wire cables go, must be rewired.  The new meanings will be: 


Black -- always-hot (no surprise there)
White -- actual neutral 
Red - switched-hot 


You must studiously follow this code everywhere in this network of 3-wire cable, or you'll get the sparky boomy.  now each device gets wired to the wires it wants: 


switches get connect 2 wires to always-hot black and switched-hot red. If you are reusing 3-way switches, make sure to use a black screw, a brass will go unused.  
receptacles get always-hot black on the brass screws, and neutral white on the silver screws. 
lamps take switched-hot red and neutral white.   They usually have pigtail wires; the black or brown wire is switched-hot (red).  The white or light blue wire on the lamp goes to neutral.   


After that, you wirenut-join all wires of the same color (remembering one lamp wire counts as red). 

If you have any single wires left dangling, put a smaller wire-nut on them and tape them to keep the wirenut from falling off (they love to fall off singles).