How do I replace trimmer line on a straight shaft trimmer?

Hi,
As a general rule the line wraps in a counter-clockwise direction. The spool is generally marked. Most heads are made by companies other than the manufacturer of the machine
How about brand and model
Peace,
Clarke

Hi,
I will give a link to a manual that has a good section on it.
Bolens 2-Cycle Gas Trimmer Operator's Manual | ManualsOnline (http://lawnandgarden.manualsonline.com/manuals/mfg/bolens/bl150.html)
Peace,
Clarke