The next time you work with a drive belt, timing belt, or timing chain, you’ll likely need to loosen a tensioner pulley to remove it. Following these general recommendations and specific guidelines from your own owners manual or repair manual, your belt or chain will function for the life of your car.

Toyota and other timing belt tensioners are loosened by simply removing them from the engine. You need to gradually compress them in a bench vice and lock them with a pull-pin before reinstallation.
Hydraulic (not hydraulic-damped) tensioners are nearly always Car Pulley Belt located in the timing case, mostly on automobiles with timing chains, while some are used in combination with timing belts. Hydraulic tensioners are powered by essential oil pressure from the engine oil pump and could press on a tensioner pulley (timing belts) or tension slipper (timing chain). You'll likely need the entire year, make, and model details, and you may need to use special tools for this kind of tensioner pulley.
Typically, a hydraulic tensioner needs to be “reset” and locked after removing it from the engine. Remove the lock only after the tensioner, pulley, or slipper, and timing belt or timing chain are installed and aligned.

The spring maintains tension, as the hydraulic damper keeps it from bouncing under load changes. This prevents timing belts and timing chains slapping and jumping teeth and continues drive belts from slipping and making sound. To loosen a drive belt spring tensioner pulley, refer 1st to the restoration manual or owners manual’s specific calendar year, make, and model details.
You may need a special tool, but many spring tensioners have a square hole, for a 3/8” or 1/2” breaker bar, or a hex or square protrusion for a wrench or socket. Using the appropriate tool, release tension on the belt. You'll need to hold some spring tensioners while slipping on a new belt. Others may possess a locking mechanism, such as a hole for a locking pin or hex crucial.

To loosen an NAI tensioner, loosen the locking nut or bolt, then back off the tensioner screw. Drive the pulley toward the other pulleys or components, loosening the belt.
Spring tensioner pulleys, as the name implies, make use of a spring to hold tension upon the belt. Most, if not all, spring tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more complex and costly but don’t require adjustments and are less susceptible to user error.