Can we convert Tourist Visa to Residence Visa?

I have already told you that you will not be able to change tourist visas into residence visas.  Look at the Sri Lankan government website.  It is quite clear.

If your skills are such that you can find a well paid job with a large employer your employer will sponsor you for a residence visas. But your job will have to be in a category  which the government deems desirable and in the county's interests. Sri Lanka has plenty of graduates looking for jobs. Do you have some specially desirable qualification which will compensate for you not speaking Sinhala?
I very much doubt it. And as for your wife's English teaching qualifications, Sri Lanka has plenty of graduate English teachers. Your wife's chances of getting a job which would give her a residence visa are vanishingly small.  If you come here expecting to change tourist visas into residence visas you will waste your time and your money. You will be disappointed and you will have to return to Pakistan poorer for the cost of the airfares and your accommodation.

You can only change a tourist visa to a residence visa if you are retired and can satisfy the My Dream Home requirements and have all the necessary paper work with you. As the other to responder said you cannot do it for getting a job etc