We just bought a three level house.
The t-stat is on the main level it stays quite comfortable.
The upstairs where the bed rooms are however stays pretty hot. Celing fans in every room help some what.
We cant afford to crank it so cold to cool the upstairs. Plus it likely will make the main level an ice box. We just got a all new HAVC so any upgrades there would just be silly.

Any tips ?

At my house the system is set up with two vents in the upstairs room and the rest on the main floor. In the summer and winter we have two diffrent settings. They have installed a unit that allows us to go under the house and controll how much air flow goes to the rest of the house. In the winter we keep it mostly set for the main floor. The heat rises and i like it cold up there anyways. During the summer we have it set for more to flow upstaris. It really is nice to have.

Shut down some of the vents downstairs. That will force more of the cool air out of the upstairs vents.

More insulation in the attic or an attic fan (if you have an attic) will help quite a bit. We installed an attic vent fan in our house, and it dropped our upstairs temperature about 5-10°.

Listen to this they describe how to balance out your system.

http://toolmonger.com/2007/05/09/one-beer-projects-balancing-your-ac-for-the-summer/

Check the air handler. The newer system have a duct setting for winter and summer. The setting will divert more air flow to the up or downstairs. Look for a small lever handle on the side of the air handler duct.

Incandescent bulbs which are high wattage, and spot lights produce a lot of heat. You could use fluorescent, or LED bulbs to lower the heat. Get dark or thick window shades to keep sunlight from turning the room into a greenhouse.