xcode - Can't uncheck constrain to margin -

when trying put imageview inside custom cell ,i wanna image take spaces in cell without margin. found there grey margin on left of cell.

i thought problem of constrain margin checkbox seems grey, , keep checked if uncheck it.it checked status... can't uncheck it, , uncheck relative margin on constraints, didn't work either... i'm confused.

thanks ur help.

try setting constant value of margins -16