For ranged, run away while shooting him. He is weak to pierce damage, so that should help.

For melee, use the spear, and preferably a shield. If you have a bronze buckler, use that, otherwise probably best to DODGE his attacks instead of trying to block or parry them. The dodge roll does have some i-frames to it, so just because a troll's attack should hit doesn't mean it will if you time it right.

The rest is just being persistent. They will go down, you just have to get used to dodging and moving defensively.