2002 celica GTS Transmission makes noise when shifting souns like gears grind although clutch is pressed all the way down. Do not see where to check tranny fluid. I replacing the clutch difficult on this car?

There may be several reasons for this. 1st, low transmission fluid levels can cause the gears to grind while shifting due to lack of lubrication. I would suggest checking the fluid level, there is a plug located on the side, in about the middle of the transmission which when removed should slowly seep oil from it. If it doesn't then you will need to add the recommended transmission fluid.
2nd, a maladjusted clutch can cause the same problem. Even though you have the clutch pedal to the floor, the clutch pressure plate may not be completely disengaging from the flywheel. This will cause pressure on the gears and synchronizers while trying to shift. I suggest having the clutch adjusted by a mechanic if you have never performed this function yourself. An inproper adjustment can severely shorten the life of the clutch.
The 3rd option may be a warn clutch component like the slave cylinder if equipped, the throwout bearing or even the pressure plate itself.
A visual inspection can be made of the clutch by removing the inspection plate from the bottom of the bell housing to view the flywheel and clutch. With someone depressing the clutch you should be able to see the clutch moving off the flywheel.