Changing matter into energy

So like Einsteins $$E=mc^2$$ formula states that if we have any mass (m) we can convert that mass in an energy by multiplying it with the speed of light(c) squared. I read on some area that if we add 90megajoules of energy to an object then its mass increases by 1microgram!, If you see a chunk of R-candy and give it an amount of heat energy, it will start to combust and while it combusts it will lose its mass and dissapear, only abit of burnt thing is left(1/20th o the mass), So my idea is that if we give A large amount of energy in a specific form, maybe we can change the mass to energy, so like if we have 1kg of mass, einsteins formula says multiply by $$c^2$$ so maybe we collide the mass with photons with the energy of $$c^2$$ or maybe somme 300000000 photons and we can change the mass to energy,