Is an upper ball joint threaded?

Service Manual should have a Schematic Diagram.
Free Manual
http://www.autozmagz.com/search/1990+dodge+ram+250+van
Also
http://www.auto-repair-manuals.com/1990_Dodge%20Truck%20Van%20SUV_Auto_Repair_Manuals.html

Yes
Watch the job on a You Tube Video &
do upper & lower-- both sides,all 4 ball joints

REMOVAL AND INSTALLATION Upper ball joints are not replaceable. The upper ball joint is part of the upper control arm bushing joint and is not serviced separately. If the upper ball joints are found to be defective, the entire upper control arm bushing joint assembly must be replaced. Lower Ball Joint INSPECTION

1. Support the vehicle in normal driving position with ball joints loaded.
2. Wipe the grease fitting and checking surface, so they are free of dirt and grease. The checking surface is the round boss into which the grease fitting is threaded.
3. The checking surface should project outside the cover. If the checking surface is inside the cover, replace the lower arm assembly.

HIT with a big Hammer on the side of the ball joint metal, then it come out by itself.

The upper and lower ball joints are riveted in on the oem ball joints you have to cut the rivets and then use a balljoint press to press them out the new ball joints have nuts and bolts just press them back in and tighten down the nut

If you turn the steering one way fully, looking behind the front wheel, you will see a pair of ball joints, one above the brakes, and the other below, very close to the wheel.
They are each attatched to a wishbone shaped component.The upper and lower.

yes. try your tool dealers or tool rental

 just tare the axels down and pull the brake callipers and brake disks, to get to the ball joints. un bolt the nuts and take the peice holding the ball joints in and  then press out . But you need a ball joint press if you wanna do it on your own

That works fine on a relatively new vehicle but one that has run in salt etc you'll save a lot of time if you remove the steering knuckle completey by separating lower ball joint and outer tie rod end ball joint and bring the whole steering knuckle to a bench to separate the hub/bearing. Soak everything with penetrant, loosen the bolts a few turns and try hitting right on the bolt heads. I also made a very sharp wedge from a chisel and rammed it hard on the other side to seoarate the hub. It will finally come apart then you'll see all the **** that was binding it due to an alumininum knuckle re-acting with a steel hub. Clean the hole and grease everything and fit new bearings

Hi my name is Allen!

Yes there are 2 tools you will need.
1- C-4212F Ball Joint Remover and Installer
2-DD-1278 Coil Spring Compressor

Be very careful as these springs can be very dangerous.

Good News: You should be able to rent are they may even let you borrow them at AutoZone or some other auto parts store.

For further asistance you may reach me at FixYa!