I repainted my bike recently. I used paint stripper.
Any kind will do. Just get stuff that works on steel.
Apply generously and wait for it to bubble and blister.
Then when it's blistered, you can take a wire brush to it.
I think a drill with a wire brush attachment would be a lot faster.
Be prepared to spend a lot of time sanding.
I went for bare metal. So I used heavy grit wet/dry
sand paper douced in water.
You can do what I just said or get it sandblasted which saves a lot of time.
It took me more then 2 hours to strip and sand my frame and fork down to metal.
After that primer. Spray can, hold it far like more then 12" away.
Best to do it on a non windy day with lots of ventelation.
You'll have to do many coats if you want it even.
Best of luck.