DHIS 2 - How can i access this web application in customize Form :

Dear Sir,
How Can I access DHIS-2 Web Application To Change Its interface According to my Needs.

For Example :

The Organization Unit Tree :

**- Will I change it from Frond End by using Javascript or HTML/CSS. **

- Will I access it through bekend ? using Java ?

Kindly Guide to me a way to access it and can be able to change it according to my need. Especially The Organization Unit Structure.