1. Remove the Y-belt and access tensioner
Move the heat-bed backward to expose the Y-axis front cover; remove the small cap covering the tensioner screws. 
Use an H2.0 mm hex wrench to loosen the two tensioning screws by one turn (do not fully remove them yet). 
Remove the belt fixing plates and the belt if needed to gain access to the tensioner. 

2. Remove the old tensioner
Using the H2.0 mm hex key, remove the four screws securing the Y-axis tensioner. 
Remove any spring hook connected to the tensioner (often 2 screws) to release it. 

3. Install the new tensioner
Position the new tensioner unit in the correct orientation over the belt and base. 
Secure with the four screws you removed earlier (use correct torque but avoid overtightening).
Re-install the spring hook and tensioner screw if required.

4. Reinstall belt and final adjustments
Re-thread the Y-belt correctly through the tensioner, idler pulley and attach it to the heat-bed bracket. 
Tighten the two tensioning screws: manual move the heat-bed back and forth along Y-axis three times, then tighten screws fully. 

5. Verification & calibration
Power on the printer. Manually move the Y-axis to check for smooth motion without catching or stiff spots.
Perform the printer’s “Vibration Compensation” calibration routine to ensure everything is aligned.