Varnishing already varnished handrail and bannisters...? What's the best way to varnish my already varnished handrail and bannisters...

What's the best way to varnish my already varnished handrail and bannisters on the stairs?

They are a fluffy pine colour but I'd like to varnish them a dark (mahogany) colour...do I have to sand them down first and what's the best type/make of varnish to use?
Re-Doing my room (!)?
Answers:    sand them first, start next to a 80/100 grit, then do a 150 grit and finish them next to a 220 or 250. I prefer minwax. You will need 2-3 coats of stain. Then 2-3 coats of polyurethane. it will be easiest to apply beside a new verbs rag.
How to sort a Christmas tree stand from...
Get some sand thesis what they call flour weekly.It is very fine and give off a slight rough dust when using it.Do not try and stain the wood,it will just crust off.Buy a dwindle with the stainers built contained by.