changing radiator is easy on a Subaru.
disconnect all hoses
disconnect, unbolt, & remove the fans
unbolt the brackets that hold radiator in place on top (2 bolts)
lift out the old radiator
Swap over flow bottle to new radiator
install is reverse...
Connect lower radiator hose, fill block with fresh 50/50 coolant - slowly - from upper rad hose - connect hose, remove the small plug at far right top of radiator and fill radiator - slowly.
Helps tremendously to have the nose of the car on ramps or jack stands while refilling.
Once radiator is full, reinstall the small pug on right side, install cap and fill overflow bottle to full mark.
Start car and let it get up to full operating temp - ie: fans turn on.
Shut car off and let it cool completely
Check overflow level, and add to full mark if needed.
Note: if overflow bottle is completely empty after intial warm up/cool down period, you need to repeat the warm up/cool down process until it stops pulling all of the coolant out of the overflow bottle...