Never open a tensioner assembly to repair internal parts. The spring is powerful and preloaded and may cause serious injury. Worn tensioner assemblies should be replaced with a new assembly, since there are no serviceable internal parts. Only pulleys can be replaced.
Because tensioners are vehicle-specific, there is no universal replacement procedures. On some vehicles, tensioner replacement is a simple as removing one bolt, while other vehicles may require removal of several parts to get to the tensioner base. Refer to your vehicle's service manual for replacement procedures and bolt torque recommendations.
When replacing a tensioner, belt and fixed idler pulley replacement is also recommended (if one is used). A used belt will function properly with a new tensioner, but belts and pulleys have generally reached their useful life expectancy when the tensioner requires replacement.