Hello, bbevrotte! Welcome to the forums...Since you didn't get an immediate response, here's my take. First off, according to Mopar parts references, the upper control arm with ball-joint is a single, unit-piece replacement item: Mopar Part #52090206AF or the current supercedure. If that's true of the aftermarket, you're replacing the arm as a whole and not just the ball-joint. Look into this and let us know. If the ball-joint is a separate replacement item now, continue as I describe below...Here is the parts schematic (zoom into the page for detail) that covers your WK Grand Cherokee:
WK Jeep Grand Cherokee Front Suspension Parts.pdf 139KB
If you review the lower control arm ball-joint steps at the top of this topic, you will see that the task for the upper ball-joint would be the same through Step #4. First, I would make sure that you have the C-press and tools. (For occasional use, Harbor Freight has a nice knock-off kit for both a C-press with sleeves and a 4x4 additional sleeve kit to round out these tools. The 4x4 kit is more for beam axle ball joints, though you might find the sleeves helpful.) Prepare for removing the control arm but don't do so unless you cannot get the C-press to fit safely on the ball-joint of the upper control arm.
After loosening the upper ball-joint stud, you should have decent range of movement at the upper control arm. If enough range to get the C-press into position with the control arm still attached, simply remove and install the ball-joint. If not, either remove the upper control arm or, if somehow easier, first remove the knuckle and half-shaft.
A General Ball-Joint Warning: Always be clear whether a ball-joint is a press-in type or a thread-in type. Do not force a threaded ball-joint loose with a press or C-press, you will ruin the control arm or beam axle! Use the proper size and type socket on a threaded ball-joint. Click here to see an example of a threaded ball-joint application for a Chrysler passenger car or IFS light truck. At the lower part of the article, you'll see the OTC ball-joint removal socket. Note that the ball-joint will have a hex-head or similar means for rotating the joint with a specialty socket. If there is simply a shoulder that accepts a press sleeve, with no flats or slots, the ball-joint is a press-in type.
Let us know how this works. If you encounter any difficulty, post here, and we'll walk through the installation. If this turns out a straightforward project, please share your findings and results. Let us know your Grand Cherokee suspension is safely back together!
I'm quite puzzled why we're replacing ball-joints on these '05-up Grand Cherokees already. The beam axle WJ steering knuckle ball-joints would last for an incredibly long while, like other beam axle parts. What's with the ball-joints on these later IFS models? Is your vehicle modified/lifted? Oversize tires? How many miles on the odometer now? Driven off-road a lot?