what the title says, how can I edit a bomb to make a more powerful explosion?

Visually, or in terms of damage? In either case, just edit the particles involved - make them go faster, live longer, and so on. You might need to make custom particles that are heavier and/or sharper for damage, or have their own sprites/etc. for effects.

Alternatively, spam some 9s in the count of particles gibbed, that should make you kill vanilla stuff without problems.

Now, if you really want to rape everything, it's much better to create your own particle.