How do I change the coolant on this it's a 1999 I think it's a 250 how can I tell and how can I get a user manual for servicing thanks

Under the tank there is an inlet for the coolant. Open it with a big wrench.

 

To let it off you could take a coolant hose of the waterpump (or the pump for inspection) and let it out. Although nothing really happens to the pre-pro engines concerning the coolant system. Only sometimes problems with the fan or thermostat. 

A lot of information can be found on gas gas USA website http://www.gasgas.com/tech.htm

Everything you need. http://www.trialspartsusa.com/tech.html