This is the simple, "I assume you have the aptitude to figure this out and anticipate the pitfalls before you jump into them" version of this tutorial. Have a look here for the long winded  version first:

Seiko 7a_8 quartz chronograph Crystal replacement and info

tools you will need:

Watch crystal press

Jewelers Screwdrivers

metric dial calipers

 watch case back removal tool Jaxa type for most brands except the Rolex style

You can see some photos of my amateur workbench and tools here: Workbench

 

choose your victom

size a cuped die to fit on the bezel so there is room for the crystal to be pressed out

there perfect fit

place the cuped die on the bottem

inside of the victom.

need to find the stem relese so the crown and stem can be removed so the movement can be removed

there's the release

crown and stem are removed

notice the plastic movement retainer that holds the movement centered in the case. you may have a metal one and or screws with little clips that stick out against the case to hold the movement in place

movement is out watch case is ready to have the crystal replaced

pick a die that will fit through the watch and press against the crystal

without dragging on the inside of the case

chuck it all up in the press like so

Gently press down, if nothing happens press a little harder

"pop" its loose

measure the old one

30.5mm!

measure the new one

30.5mm

chuck up the dies for the reverse a die that fits the crystal on top this time.

normaly you would use a flat die but in this case Im useing a cuped die to press it in with since there is a cyclops magnifing eye on the crystal.

Pick a die to hold the back of the watch too

be carefull that it actually holds the watch flat around the caseback hole. if the die holds the watch up on the lugs it may cause problems

after a little repeated pressing turning of the watch head and patience its seated evenly and ready to go ..

now just put the watch together and your done!