Is shifting career from IT support to IT sales a good idea and if yes how can you get in to IT sales?

Depends on the years of experience you have. Also, sales is completely about your network in market.

If you are at early stage like 3-4 yrs in industry then its okay...

if you are 6-7 years and now taking a leap of faith, will need lot of efforts 

Indeed its a very good idea,rapid growth,both technical and sales skills are utilized.