Fast picking advices

I've been playing guitar for a year, just learning the tabs to songs that I like. My main problem is speed. Playing solos like the one in 'Stairway to Heaven' is much easier for me than playing the solo in 'Iron Trooper', for example. The problem is switching between strings at high speed and playing fast licks. Maybe you have some advices to gain more speed, especially on higher tones lower then 12th fret