How do I change the active element of the Murmur fusion rifle?

Question

Having recently completed some of the The Dark Below story missions in Destiny, Eris Morn gave me a special legendary fusion rifle, the Murmur.

It says that it can toggle between arc and solar damage, but I've pressed every button and combination I can think of and haven't had any success.

How do I toggle the elemental trait of the Murmur?

Answer 1

You have to go into the weapon's upgrade screen and toggle it manually. Should be unlocked right from the start.

Answer 2

Open your inventory, press Y/Triangle on the weapon, and toggle the active element on the far left as if it was an upgrade.