diff --git a/.travis.yml b/.travis.yml
index 5feed29..3cba66c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ before_install:
 install:
   - pip install pycurl flake8
   - pip install mock
+  - pip install six
   - python setup.py install
 script:
   - python -W always setup.py test
diff --git a/README.md b/README.md
index 5ee32e3..e302f57 100644
--- a/README.md
+++ b/README.md
@@ -214,7 +214,13 @@ account = customer.back_accounts.retrieve("bsbg7igxh3yukpu8t2q4")
 Add subscription to customer
 
 ```python
-customer.subscriptions.create(plan_id="pbkliysxavp8bvvp8f0k", trial_days="5", card_id="kvxvccpsesm4pwmtgnjb")
+customer.subscriptions.create(plan_id="pbkliysxavp8bvvp8f0k", trial_end_date="2023/12/31", card_id="kvxvccpsesm4pwmtgnjb")
+```
+
+Get customer subscriptions
+
+```python
+customer.subscriptions.retrieve("pbkliysxavp8bvvp8f0k")
 ```
 
 Cancel subscription
@@ -234,7 +240,16 @@ Update subscription
 
 ```python
 subscription = customer.subscriptions.all()[0]
-subscription.cancel_at_end_period = True
+subscription.cancel_at_period_end = True
+subscription.save()
+```
+
+Change subscription card by token
+
+```python
+subscription = customer.subscriptions.all()[0]
+subscription.card_id = "ppldmckf6ls94skdihkd"
+subscription.card = None
 subscription.save()
 ```
 
diff --git a/openpay/util.py b/openpay/util.py
index 40de5d8..c3a8d2c 100644
--- a/openpay/util.py
+++ b/openpay/util.py
@@ -1,14 +1,15 @@
-
 import logging
 import sys
 
+import six
+
 logger = logging.getLogger('stripe')
 
 __all__ = ['utf8']
 
 
 def utf8(value):
-    if isinstance(value, unicode) and sys.version_info < (3, 0):
+    if isinstance(value, six.text_type) and sys.version_info < (3, 0):
         return value.encode('utf-8')
     else:
         return value
diff --git a/setup.py b/setup.py
index 9db965c..992d6ee 100644
--- a/setup.py
+++ b/setup.py
@@ -43,5 +43,5 @@
       package_data={'openpay': ['data/ca-certificates.crt', '../VERSION']},
       install_requires=install_requires,
       test_suite='openpay.test.all',
-      use_2to3=True,
+      # use_2to3=True,
       )