How to merge company codes

Dear Friends

i have one complex issue we need to merge with company codes, how, what are the step need to follow

1, we have 3 company code like 2000, 2100, 2200 but need to merge with 2100 and 2200 to 2000 company code

2, Chart of account is same all the company code

3, Controlling area is same all the company code

4, GL, Customer and vendor is same number up to 95% all the three company code

5, same similar business in all the company code, we are using SAP near 7 years

Please suggest how to merge

Regards

Jaikumar.P