How do I get the old line trimmer spool off of my Ryobi 18 volt cordless trimer

SOURCE: ryobi weed trimmer

I have one of this trimmers. It is simple to replace the line. 
-First line up the arrows on the bottom of the spindle. 
-Then feed the line back in one of the holes in the side of the spindle (this is the same hole that the cutting string comes out of). 
-You will see the line come out of the bottom of the spindle. 
-Take that line a place it in the hole on the bottom of the spindle. 
-Leave about 9 feet of string hanging out of the weed eater (do the same with the other side). 
-Then turn the inside wheel (I can't remember if it is clock wise or counter clock-wise but it will only turn one way) most of the string is rolled into the spindle. 
-Cut the string of about 5 inches out of the weed eater. You're ready to cut!

SOURCE: Ryobi Electric string trimmer

TJ, I've had the same problem since yesterday and I found the solution (lots of googling - that's how I found your post BTW).
It turned out that the switch malfunction is a common problem.

The part number for the FA3-4 switch is:

ut41002a-36 ("switch assembly")

Available here (thru Amazon):
http://factorylawnandgarden.com/product/553902/B000PLVCX8/SWITCH_ASSEMBLY_UT41002A_36/

It's a Homelite part, which is identical to Ryobi.

Here is the manual showing it (part 6):
http://www.m-and-d.com/pdfs/ryobi_tool/RY41002.pdf

Here is the thread with the solution:
http://www.ryobitools.com/dc/dcboard.php?az=show_topic&forum=112&topic_id=597&mesg_id=597&page=3

HTH,
Adi

SOURCE: Ryobi Trimmer

To install string in the Ryobi you do not have to disassemble anything: Line up the two arrows on the inner and outer reel, remove any excess string, cut two pieces of string about 10 feet, feed line in the side holes, secure line in hole where it comes out the bottom (it only takes about 1/4in. to do so), pull strings tight, then turn the inner reel counter clockwise to wind it. If it sticks a little just pull line a little.
To remove the inner spool in order to remove line that has broken inside, to clean the mechanism, or to perform other maintenance, grasp the outer reel and unscrew the bump knob counter-clockwise. Mine is often very tight and requires pliers to get enough leverage. While you are in there, clean the inner reel and the inside of the outer reel to improve feed performance. The shaft rarely needs cleaning. Do not lubricate. After re-installing the reel, add string (0.080") as described above.

SOURCE: Replacing Drive Shaft for a Ryobi 725r

The lower flex shaft should cost around $40, unless you order it online and have to pay shipping. You should be able to get one from your local MTD dealer. (Ryobi is owned by MTD)

SOURCE: Need routing of fuel lines on Ryobi string trimmer Model 725R.

The larger fuel line goes from fuel filter to carbuerator.The smaller line is the return line from the purge bulb tofuel tank. mitchjl_1692