I have the brushed A-10, and also have a power problem. I live at about 7,000 feet in the mountains, and do not have enough power to
lift off. I have tried, and all that happens is the nose will lift, and the plane will run with the tail on the ground! I tried a heavery (bigger)
battery only to have the speed controller quite.
What I want to know is, how hard will it be to convert this plane to a brushless version? Also can I get a replacement speed controller to
replace the one I messed up?

Just curious, how much experience do you have flying RC planes??

I have been flying r/c since 1975, and am an instructor, and test pilot.

Replacing the EDF motors is doable but not easy.

In your shoes I'd get a new brushed ESC ( they are cheap ) of slightly higher capacity than the one which is included, that supports LiPo packs. Many do either out of the box or via a jumper or switch.

Then use a 1200mAh or so 3S 11.1v Lipo pack ( you'll need a charger for LiPo too ).

This will produce MUCH more power from the motors.

Note the brushes will wear faster, but they will probably outlast the plane never-the-less.

Just avoid flying the plane at full throttle after the conversion. Give it enough to get up and then try to keep the throttle below 80-90% after takeoff with this combo.

You'll be driving the motors at higher voltage, but they will tolerate it.

They'll tolerate 11v+ for short bursts. You just don't want the windings to get hot and burn out.