Dear Friend,
I did the same..Do these things..First u hv to make new contract with company with new salary and Position. Also u need a letter from ur sponser stating that u r working in his company as "Engineer" and his current salary is QR.xxxx .
make 3 copies of your new contact and old contract. and u hv to get 3/6 months Bank statement and letter from Bank stating that u account receiving said amount (it should be same as the amount mentioned in the new contract". Bank has to put seal for these documents.
Then u hv to get seal from labour contracts. there u hv to pay 60 QR. then submit application with these documents to Labour.. then wait for 7 days. if it is approved u can submit the same to Immigration. They also approve that..if they dont hv any problem, u hv to pay there QR. 300. they they will issue new ID with ur new Proffession. all procedure it wil take max 2 weeks if ur all documents are ok..Pls note that you must need Bank statment and New contract.

If u hv any doubt, call me 5463993

Biju