Replace / Upgrade a Tourney drivetrain

I've worked on bikes for years, but never previously sunk to these murky depths. Please can you help with what may seem like nupty questions.

A friend has a 3x7 speed Tourney system on his commuter and it's utterly worn out. We need cassette, chainrings/chainset, chain, jockey wheels. Or, would it be better / cheaper to replace with a 9speed system ?

I'd appreciate your advice and any pointers as to where to get this stuff cheap.

I believe it has a screw-on cassette, can I remove this with my trusty Shimano lock-ring tool ?

Thanks in anticipation.

I suspect a new (or newer secondhand) bike will be cheaper.

I believe it has a screw-on cassette, can I remove this with my trusty Shimano lock-ring tool ?

no, there's a different tool with longer/shallower splines for the freewheels

If the bike came with an all tourney setup, it's probably not worth much more than £300 anyway, and to put anything decent on would require a rear wheel upgrade aswell, so probably not worth it imo. You could spend £100 on parts easily and never see that money back

I'd stick the bike on ebay as is and get £50 for it, and put it towards the cost of a new bike.

Or buy the Acera group off this guy.

http://www.lfgss.com/thread124988.html

new cassette (freewheel), stick with 7 or lower, use a new chain and go single on the front

don't worry about the jockey wheels, it doesn't matter till you spend £££