opencart plugin

Hi I want to connect this xml https://www.zougris.gr/Content/files/ExportImport/xmlfeed.xml with this site www.e-dokimes.eu after the products will be updated automatically , and it must be made that I can adjust the percentage on the prices for all its products from this supplier and in product/data must put a fild to to add cubic because after the metaphors will come out the basis of this field if need plugin I buy it site is in journal 3 the work will have to be done with me to see thanks