My printing output is not as dark as i need it be, compared to other printers.
Is there a way to make them darker?
The toner is at 90% so that is definately not the problem here.
In print driver, at Printer Properties, select Print Quality then select High Resolution and in Color Options tab select Color Adjustment and make adjustment.
This is because Microsoft do not have a specific driver for Windows 10 for your machine (is too old). But i thinking and it is possible your issue to be a hardware one, for example from black developer housing. To see that print an A4 with 60-70% black coverage and put a image here.
It could be a machine xerographic issue if copies are also light. Is it only in black? It may be time to have the black developer housing replaced.