Unscrew the metal plates, then wiggle the pre amps out.
I shouldn't post when drunk..

15 Jackson SLATHX-m 3-7 Slime green
Squier std tele (modded to hell)

Engl Powerball
Laney Ironheart 60h
Zilla Superfatboy 2x12 v30's

You just need to GENTLY rock the tubes side to side / back to front and pull them straight down - they're just stuck. Nothing to unscrew. I thought I was going to break the glass the first time I took my tubes out - they may have been original when I replaced them 6 months back. . . . Once you feel one give you'll be good.

The issue is the pins have corroded into the sockets. You'll need to get some good contact cleaner like DeOxit D5, spray the new tube pins, and work the new tube in and out of the socket until it goes in easily to clean up the corrosion and get a good seat on the new tubes. If you don't the new tubes won't get a good connection and life will suck.
Ibanez RG1570 Prestige
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .
Quote by Carrot
Unscrew the metal plates, then wiggle the pre amps out.

I feel like this might be right...I can't seem to pull it out.