How to change internal oil filter on 08 toyota sienna

how many miles are on the car?

so if the level is good on the dip stick , and you changed the filter
the next obvious is the level sensor is bad.
after that your looking for internal engine problems

Exactly five quarts to do an oil change on this van assuming you are also replacing the oil filter.
How long between oil changes is typically recommended to be 5000 miles by Toyota. The van's service reminder light comes on at 5000 miles just for this purpose. To increase that interval is your choice.

Special Service Tool from Toyota is part number 09228-06501

use 10W30 oil, any brand, any parts store can supply the correct filter, fram is a good brand

Every 3,000 miles or every 3 months, which ever comes first.
If you need the type of oil, look in the owners manual that's in the glove box, that will show what type of oil to use.

get underneath and look for it. the plug will be on the bottom of the oil pan in the sump portion. the filter will be readily accessible from the underside of the vehicle as well, possibly concealed underneath a cover or hatch.

a local auto parts store will have every thing you need including manuals

You still have to drain the engine oil from the drain plug in the oil pan, and I recommend replacing the drain plug gasket.
If you buy a filter from Toyota, it actually comes with instructions on exactly what to do. There is a 3/8" recess in the bottom of the filter housing, when you put a 3/8" extension and a ratchet in this and remove it, there should be a plastic piece that comes with the filter to pop into the bottom of the housing and drain the oil. replace the o-ring and reinstall the housing drain plug.

You can get a filter-cup tool from Pep Boys or local auto parts tools sections that will fit the filter housing. Use the cup with a ratchet and extension to remove the filter housing. replace the filter cartridge and the o-ring. Make sure to lubricate o-ring, they will snag! Reinstall and add 6.4 qts of oil