Window tight to shut

[theremotedr]

I have replaced the handels & gearboxes on th upvs windows as the previous owner never opened them and they were stuck.
I have them working now 100% but when i close the window and try to pull the handle down to lock it the force to do so is very very hard/tight.
If i remove the metal keep that is screwed into the window the operation is like it should be,nice and smooth.
Please advise what i need to do to the metal keep in order for it to be working correctly.

Thanks

[welsh brickie]

on the window mechinism there are rollers these can be ajusted using allan keys they need to be turned slightly to achieve the correct tension and grease it well once finished