How can i make clutch pedal lighter

i only know of an "easy clutch pressure plate" that can be switched out for some money.

 

because 2015 has hydraulic linkage(possible with air assist) and 2000 has mechanical linkage. When you change the clutch get Eaton's Easy Pedal clutch

 

that's the name i could not remember, thanks

 

All Volvo's from 1998 to the present came with a hydraulic clutch.

If you want a easy clutch, you need to install a Easy Pedal Advantage Clutch from Eaton.

 

Late 80's and into the 90's Autocars had a similar system with no cable. I thank they had a hydraulic set up to control the air system. That maybe fairly easy to install on your truck if you can find one in the bone yard. Cableguys is an interesting set up and would be all new.
If Volvo made one with air assist, as mhyn said may have been, you should be able to find one of those used. It will definitely fit your truck. Parts are available locally. If you do that get and keep the serial number of the truck it came from.