It's really easy. All you need is some 5/8" heater hose, some hose clamps, something to cut the hoses, and something to cut the valve off of the (metal) tee.
I bought a used valve from the j/y ($6) and built the new assembly before removing the existing valve/tee.
Cut the valve off (be sure to file/clean the cut end) and measure/cut and attach new hose pieces to the 'new' tee. Measure by holding the bulk hose where you want it, and mark your cut. make sure to leave enough to go past the old valve and onto the tee.
Removed old heater valve and hoses.
Replace existing valve/tee with new assembly.
Measure twice, cut once, or buy enough hose to do it again.
Here's a good time/opportunity to back flush the heater core.
If you're even mildly mechanically inclined, then I wouldn't think you need much more write-up than that.
