You need to put a bleed port in your system at the high point. We generally do this as follows:
1. Use a radiator with multiple ports such that you can open a port on the top rad. Using a 40mm G-1/4 extention ... I extended py rad fill port to just beloe the case grille with a cap. Then assembled a 12' acrylic tube with two G-1/4 fittings. To bleed, remove the cap, screw this into the top rad's top port. Place a Valve at the top (I used all Bitspower tube adapters and fittings) with a funnel on top.
2. I would also suggest switching your reservoir top to a 3 port model. On the top inlet, extend a fill tube such that your discharge extends below the water level. The standard part is about 4" long and you'll want it submerged about two inches, leaving some air space on top. On another top port I made a small riser G-1/4 screw fitting 20mm extension and another valve.
3. We also use a 12V source and leave system off powering pump only ($15)
4. One more tool ... assuming the bleed port is at the back of case a 2" thick book under the back end will cause all air to collect at the back of the top rad.
5. Open the valve and pour water into the funnel filling the tube about half way. Close the valve and run pump. As water is circulated, trapped air that frees itself will be trapped at the elevated and of the to radiator and escape into the tune, and allowing water to flow down into the radiator. Over time you can put some more water into the funnel, crack the valve open and allow it to refill. Rin the system like this until there is no change in water level.... Give the system a few shapes and tilt in all directions to free up any entrapped. air.
6. If ya did all this right, your 'fill tube will still be sticking out of th top of your case, half filled with water. Turn the system / pump off Open the valve on your fill tube. Now slowly crack the 2nd valve on top of yur res to allow the tune to drain into the system. Stop just as you reach the level of your port riser. I can send ya a parts list if ya need and a few pics
