This page explains which immigration categories you can switch from into Tier 2 (General) of the points-based system, if you are already in the UK.
You can switch into Tier 2 (General) from the following immigration categories:
If you are not in any of these categories, you must leave the UK and make a new application at your local entry clearance post.
You can claim 30 points if you are switching from:
You must have worked for your current sponsor for at least six months immediately before the date of your application. You must be applying to continue to work for your sponsor in the same job you are doing on the date of your application.
If you have not worked for your potential sponsor for at least six months before you apply, your sponsor will have to meet the resident labour market test unless the job is on the shortage occupation list. You will not be able to claim points for switching from a post-study category, but can claim points if your sponsor has met the resident labour market test.
This is the process an employer must follow before employing a person who is not a permanent resident of the United Kingdom if he/she is first required to show that no resident worker could be found to take a job.
Specific types of work that have been officially listed as ones for which there are not enough resident workers to fill available jobs. Employers who wish to hire a worker from outside the European Economic Area to fill a vacancy that is on a list of shortage occupations may do so without carrying out a resident labour market test.