If you want to exceed the limits in the PC GUI, to allow flight beyond 1000m above takeoff point, you will need to contact Yuneec.
What people are trying to tell you is that flying above 120m in many countries is illegal and can result in fines or even prison. Even licensed pilots are required to fly 'line of sight' - that is, they can see what the drone is doing. Flying above 1000m is probably beyond line of sight.
In addition - a lot of governments are looking at restricting or banning drones, due to fears of accidents and reports of drones hitting aircraft. If you fly above 120m you are in commercial air space and you could be giving the authorities another reason to ban drones.
There are occasionally reasons why you may have good reason to fly beyond the normal limits of your drone. However, unless you are a professional, with an appropriate license you are likely to cause damage to the reputation of drone pilots. You may also harm, injure or kill people if you are not in full control of your drone. Please fly safely.
Finally - in purely practical terms, high altitude flights are difficult due to battery limitations. Drones actually come down a LOT slower than they go up. This means that it is easy to run out of batteries when you are descending from high altitude flights. A drone without a battery is lethal.