If you have to press very hard on the pedal to brake, you should check the operation of the servo cylinder.
With the engine off, fully depress the brake pedal at least 5 times, then, keeping the pedal depressed, start the engine. With the engine running, the pedal should go down under foot pressure.
If this does not happen, disconnect the vacuum hose from the servo cylinder and start the engine. Put your finger on the end of the hose to check if a vacuum is being created.
If there is no vacuum, check the hose for leaks or damage and replace if necessary. Tighten all clamps.
If vacuum is present, it should be measured and the servo cylinder replaced if necessary (work is done by a specialist).