How easy is it to change the hydraulic lift supports on the trunk door of an '09 Toyota Sienna?
As easy as finding a replacement, whether online (ebay, amazon) or an auto shop like autoZone which sells such parts and then taking a star key or a rachet set to unscrew the hydraulic lift on one side and then move on to the other side when your done.
Would recommend you use a piece of wood of some sort or a ladder to support the liftgate (back trunk) from closing on you while doing the repair. "Safety first"
The bolts might be a bit hard to loosen, was extremely snug when I tried to loosen them on my car. If a hand screw driver doesn't work take a rachet with the correct bit, and try not to strip the screw or else your going to need to drill it out which is not something you want to do if you don't have to.
Or if above doesn't work try a breaker bar or a pipe over the rachet for more leverage and if that doesn't work try WD-40 or some lubricant and let it sit for a bit and then try and if still not a plain old torch to heat up the nut/bolt. Again be careful not to strip the bolt on the removal nor on the installation.
Easy fix if you have the correct tools.
Good luck.
ETA: I see all you need is a flat head screw driver and pry it right off, really simple.
Check out this video where he demastrates how to do it.
And a link for the product on Amazon.
https://www.amazon.com/s?k=power+liftgate+strong+arm+6140&i=automotiveOr walk into Auto zone and give them the year, make and model and they'll tell you exactly where to find a new pair.
Here's some of them listed on their website.
https://m.autozone.com/collision-body-parts-and-hardware/lift-supporthttps://m.autozone.com/collision-body-parts-and-hardware/lift-support/mighty-lift-lift-support/989378_53250_0?aqs=https://m.autozone.com/collision-body-parts-and-hardware/lift-support/mighty-lift-lift-support/250717_53250_0?aqs=Also seems to depend if you have a powered lift gate or a non powered lift gate.