UPDATE INSTRUCTION:
The following files has been changed in version 5.2

1. assets/js/admin.js
2. assets/js/store-v3.js
3. assets/js/store.js
4. protected/components/ajax.php
5. protected/components/AjaxAdmin.php
6. protected/components/Functions.php
7. protected/components/FunctionsV3.php
8. protected/components/InstallHelper.php
9. protected/controllers/AdminController.php
10. protected/controllers/AjaxadminController.php
11. protected/controllers/AjaxController.php
12. protected/controllers/AjaxmerchantController.php
13. protected/controllers/MerchantController.php
14. protected/controllers/StoreController.php
15. protected/controllers/UpdateController.php
16. protected/messages/en/default.php
17. protected/models/view-receipt.php
18. protected/vendor/dx-mercapago - NEW library for mercapago version 2
19. protected/views/admin/manage-language-new.php
20. protected/views/admin/theme-settings.php
21. protected/views/front/manage-credit-card-add.php
22. protected/views/front/payment-list.php
23. protected/views/merchant/user-add.php
24. protected/views/merchant/mercadopago_v2_settings.php
25. protected/views/merchant/paypal_v2_settings.php
26. protected/views/store/paypal_v2-init.php

DATABASE

1. alter table payment_order change payment_type to VARCHAR(100)
2. update view_ratings table

Run the db update example http://bastisapp.com/kmrs/update