I couldn't see a AMP section so i stuck it in general.

I've only been playing 3ish years, so i haven't had much experience when it comes to tube amps. Not too long ago, infact, comming upto a year ago, i started looking for a new amp because my marshall 50DFX was terrible. I was told about tube amps sounding better, especially when played loud so i ventured into getting a Line6 Spider Valve, even though i hadn't been a fan of the other spiders, it sounded a great deal at the time.

but already, the tubes have started popping, but looking at them they seem to look the same as when i bought it. So how do i know which out of the 4 tubes needs replacing? Or should i just save up and replace all 4?

And also, how hard is it to replace tubes, my dad a self confessed know it all, and an electrician believes he could change them even when he didn't know amps had tubes until i told him mine were stale. Should i let him have a play around or just find and pay a professional?