change the oil? Unfortunately I don't have an owner's manual.

5 qts. with filter change

Bromate, you can call the Toyota dealership and ask the parts guys or service; OR start with 3 qts, check the dipstick, and add a 1/2 qt at a time til near full on the stick. Start the truck... then top off til "full" and make a note for next oil change. Probably 4.5 - 5 qts.

try 4 then check it it maybe 5

you need to put in 4.25 qts of oil, this truck with the 2.4 engine takes this amount of oil. the only 4 cylinder toyota tacoma that takes 5 qts. is the 2.7 liter. But your truck takes 4.25 qts with filter.

as much as it needs

Toyota engine is usually a little bit less in the 4 cyclinders. I would try 3 and 3/4, then add in carefully. You don't want to add to much though.