hello,
1. You will need to make fresh visa application every time you change jobs. This might not be straight forward as Resident Labour Market Test might be required if your job is not on Shortage occupation List.
2. You can only stay in the UK under tier 2 for a maximum of 6 years. Every time you change your job and apply for a new visa, you will need to apply for 6 years minus the number of years you have already spent on tier 2.
3. From recent questions posted here, your current visa will remain valid even if your visa application for a new job is rejected as long as the new job is in the same SOC as your current job. Try as much as possible to change jobs within the same SOC if you have to change jobs, it's easier.
4. you can find SOC here.
https://www.gov.uk/government/uploads/s ... 4_V0_6.pdf