747 under 10,000 feet

I am having problems keeping a 747 stable under 250. I can't legally go over 250 knots under 10,000 ft so how do I do that?

B747 should fly just fine at 250 Kts. Check that your spoilers are retracted. The key is "/". If you use a joy stick, ensure that you have correct thrust lever travel. B747 at 250 kts will fly nose high during level flight. That's normal. Adjust thrust (power) to stay below 250 kts.

What is your payload / fuel at? If you're overloaded that could cause some of your problems. Remember, when you're landing you want ideally around 30,000lbs of fuel left in a 747 (+ extra if you didn't encounter anything unexpected). If you are overloaded you probably don't have enough lift at 250kts to oppose the gravity pulling the massive bird down!

Since you are experiencing a lack of maneuverability/lift, you should drop a notch of flaps. If you're flying the PMDG 747, you'll see the flap-speeds displayed on the left of the artificial horizon. The flaps are there to give you extra lift as the plane slows down, so that should definitly help you. There's no need to exceed 250kts because after all, the plane should be capable of flying around 180kts on final, and 140kts on the glide slope!

Just remember to plan your fuel well.

I do. Usually when I estimate fuel, I will use the checklist to know what estimated fuel I need. I will then make the fuel change a little higher and add more depending on my payload. I will note the flap method. Thanks

You can always use the autothrottle and autopilot to keep things under control