Adjusting door hinge

poppy123b

Hi there, our conservatory door is starting to stick at the bottom i tried googling and it stated removing the caps on the hinges and adjusting with an allen key. 

However those caps on our door hinge seems to be the most impossible thing to remove, which makes me think that perhaps these are not meant to be removed on this particular hinge.

So before i try to remove the caps any further and end up doing damage, if any one knows anything about adjusting doors and hinges could you point me in the right direction please

p.s apologies for the grubbyness of the hinge

531063

Caps should come off, try pouring some boiling water over them to soften them up a bit.

poppy123b

Thankyou will give it a try