Youtube is great for stuff like this. Just look up "disassemble freewheel" and you'll have a lot of hits. You can also search for a creator called "RJ the Bike Guy," who has a series of instructional videos on many basic bike maintenance topics.

Manufacturers from that era had proprietary methods, so your Suntour will come apart differently from Shimanos (and different Suntour models as well), so just be sure to research before deciding to tackle it.