UPDATE INSTRUCTION:
The following files has been changed in version 5.1

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/components/PrintWrapper.php
10. protected/config/main.php
11. protected/config/table_structure.php
12. protected/controller/AdminController.php
13. protected/controller/AjaxController.php
14. protected/controller/MerchantController.php
15. protected/controller/StoreController.php
16. protected/controller/UpdateController.php
17. protected/controller/StripeController.php - new file
18. protected/messages/en/default.php
19. protected/vendor/stripe - new Stripe sdk library
20. protected/vendor/Paypal-SDK - new Paypal sdk library
21. protected/vendor/ClickatellWrapper.php - new file
22. protected/vendor/CreditCardWrapper.php - new file
23. protected/vendor/PaypalWrapper.php - new file
24. protected/vendor/SaferCrypto.php - new file
25. protected/vendor/StripeWrapper.php - new file
26. protected/vendor/UnsafeCrypto.php - new file
27. protected/models/buy.php - new file
28. protected/models/buy_sms.php - new file
29. protected/views/admin/card-payment-settings.php
30. protected/views/admin/paypal-settings.php
31. protected/views/admin/sms-settings.php
32. protected/views/admin/stripe-settings.php
33. protected/views/admin/merchant-add.php
34. protected/views/admin/paypal_v2_settings.php
35. protected/views/front/manage-credit-card-add.php
36. protected/views/front/manage-credit-card.php
37. protected/views/front/payment-list.php
38. protected/views/merchant/paypal-settings.php
39. protected/views/merchant/payuinit.php
40. protected/views/merchant/stripe-settings.php
41. protected/views/merchant/vog-init.php
42. protected/views/merchant/stp-init.php
43. protected/views/merchant/stripe_buy.php
44. protected/views/merchant/manage_credit_add.php - new file
45. protected/views/merchant/manage_credit_cards.php - new file
46. protected/views/merchant/paypal_v2_settings.php - new file
47. protected/views/store/item.php
48. protected/views/store/merchant-signup-step2.php
49. protected/views/store/profile.php
50. protected/views/store/vog-init.php
51. protected/views/store/vog-merchant-init.php
52. protected/views/merchant/paypal_v2_init.php - new file

DATABASE

1. new fields(payment_gateway_ref) added in _order table
2. new fields(payment_gateway_ref) added in _merchant table
3. new fields(encrypted_card) added in client_cc table
4. new fields(encrypted_card) and (date_modified) added in merchant_cc table
5. new table stripe_logger

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

in version 5.1 stripe SDK is updated to latest version, please update the libray in protected/vendor/stripe,,
and old library stripe2 folder is remove on this version in the path protected/vendor/stripe2