Once you have installed HikaShop, you may upload the SageExchange Payment Plugin through the Joomla Extension Manager.
- Upload `sagepayments.zip` via Extension > Extensions Manager > Upload Package File
- Find & Activate the plugin by going to Extension > Extensions Manager > Manage
- Add the plugin through the Hikashop settings by going to Components > Hikashop then clicking through to System > Payment Methods
- Click 'New' and then click on the 'Hikashop Sage Payment Solution Payment Plugin'