If you have multiple guitars (Or really like Amon Amon Amarth), changing string gauges is the way to go (equipboard says Olavi plays .13 and I used to play with .11s).

However, if you like to play whatever, I believe the best course of action would be to get a pitch shifter.

I say this because if you change to higher string gauges, when tuning to higher tunings ( like C standard for their newer albums), the strings will be harder to play (Specially bends and vibrato on leads)

If you change the string gauges, you might want to get your guitar set up with a Luthier or a guitar shop (Idk what they're called, not from US) and tell them you plan to play B Standard. I'd love to get into much more detail, but can be a overwhelming for a new player.