Please follow the following steps to change, modify tax nambers.
- Go to "Configuration"/"Company management"
- Go to "Taxes"
- Click on the next available line (as you are about to add new tax)
- In the "Management of tax groups" window, you can modify the tax number and the GL code.
- Save and exit.
Note: In "Tax group Management" the change will not be visible right away, you have to restart the "Company maintenance" module.