This site is invaluable if you don't want to spend the $100+ on the factory service manual. I've found it to be very accurate for regular maintenance procedures. The first URL (the site's home page) has some information about halfway down on selecting the proper tranny oil, and the second URL contains the procedure for doing the change.
The hard part is obtaining the proper oil. None of the local or national auto parts stores in my area carried a decent GL-4 oil of the proper weight. I ended up ordering some Redline MT-90 online, and although it's quite expensive, it was well worth the money. My 626 is only a 2000, with 22K miles, and the tranny was already starting to get "notchy" and difficult to downshift at high speeds (especially in winter). Once I put the synthetic Redline in, and took it out for a spin, I noticed a HUGE improvement right at the first 1-2 shift.
I don't know if your '94 is the same as my '00, but my fill plug is about 1/3 of the way up on the front of the case, and it's 23mm just like the drain plug. Follow the abovementioned site's instructions exactly, and you should have the job done in minutes. The only thing I would add is don't bother with the turkey baster because it takes forever to pump 4 qts. of fluid in with one. I've got one of those flexible fluid fill tubes from Pep Boys that has a valve on top, and it worked beautifully pouring the oil into it from up where you remove the air box. Furthermore, don't bother with the regular hardware stores to find a 23mm socket for the drain/fill plugs. I had to go to a Napa auto parts store to find one, because it's a fairly odd size that isn't commonly used
Hope this helps, good luck...