Please follow the given steps :
There are three folders in exported file. One is module, second in override and third one is theme.
1.To upload a theme
(a) Copy the 'Theme' Folder from the Exported folder and Paste it at Prestashop(Root) -> Themes -> Paste Your theme here.
(b) Then from Backoffice Go to Preference -> Themes -> Add new theme -> Create New theme.
(c) Then you should fill the required fields, Theme and Directory Name should be the same as the name of the exported theme.
(d) Do select the preview image from the exported theme.
(e) Please Select the Default Left,Right Sidebars if you want them in the Theme.
2.To upload Module from Prestashop Backend Go to Modules -> Modules -> Add new Module -> Upload the module zip file placed in modules folder.
3.Please copy and merge the Override folder given at root folder.