Here are the instructions from the Ruger manual with my commentary in blue:
Use a punch to press in on the magazine spring seat where it protrudes into the hole in the magazine floorplate. Hold the magazine upside down, so you can see the Ruger emblem upside down. Put a punch in the hole which is in the middle of the black magazine base, and push. You will hear the spring compress. Slide the magazine floorplate toward the rear of the magazine, takinng care to prevent the forcible ejection of the magazine spring seat and compressed magazine spring. I push on the magazine floorplate with my thumb to get it to slide. I have never had the spring seat eject on any of my 3 magazines. YMMV. Withdraw magazine spring seat and magazine spring from magazine body. I push in on the magazine spring seat with my thumb, and get it to tilt enough that the seat clears the tab on one side. The spring will push it out once you get it clear of the holding tabs. Turn magazine upside down and remove magazine follower. Reassemble in reverse order.
Let me know if you need more detail than this. I may be able to make some pictures that show this.