Change of Employer with VISA Extention

[mahi.14]

Dear Experts,

I am on Tier 2 General VISA. I am on this VISA since last almost 3 years. on next 30 July 2014 it will expire. So i have to renew it. Mean while i found another job with different employer. So i want to transfer my visa with new company.

New company has already generated COS for me. They did UK labor market test as well.

1. So any one can please help me to understand what is next steps?
2. Do i need to extend my visa with existing employer then switch to new employer.
3. Do i need to update my existing employer for new job?
4. If i apply VISA with new employer now, will i get VISA for next 3 months as VISA is expires on 30 July or 3 Years?

Please advice me.
Thank you.