Fabrice

Hi everyone, my name is Fabrice, from south africa. im new here, and new to whmcs.... i'm a frontend developer and recently landed a project where i have to redesigned the company'system to meet their new customer journey requirements. all the work is done but the guy that supposed to upload all my work to whmcs has resigned... now the company wants me to upload and integrate the new design for them, i have access to the portal but i dont know how to go about uploading, and activating the new html files. can anyone please assist me on step by step how to do it ? i will appreciate your help so much