How to add and remove payment module restrictions in PrestaShop 1.5-1.6
PrestaShop has options with which you can set up (and remove) payment module restrictions based on different criteria. To configure these options, go to Modules menu>Payment sub-menu in the admin panel. Under the list with the payment modules there are a few blocks: Currency Restrictions, Group Restrictions, Country Restrictions. Each block lists the enabled payment modules and respectively the enabled currencies, the existing customer groups and all the countries (regardless of whether they are enabled or not from the PrestaShop options).
From the block Currency Restrictions you can choose with which payment modules can the available currencies be used. Currencies can be added and removed from Localization menu>Currencies sub-menu. From the Group Restrictions block you can configure which payment modules can each of the existing customer groups use. From the block Country Restrictions you can specify the countries with which the enabled payment modules can be used. The country of the customer's address determines whether the restriction applies. By default, disabled countries are restricted. You can enable and disable countries from Localization menu>Countries sub-menu.
To add a restriction, just unmark the respective checkbox; to remove it, mark the checkbox. If you make any changes don't forget to click on the Save restrictions button that's under the particular block.
For screenshots and some more details check out the tutorial on how to manage payment module restrictions in PrestaShop.