docs: Update "Upgrading to v2" guide (#472)

- Update "Upgrading to v2" guide

---------

Co-authored-by: Vlada Dusek <[email protected]>

Author: Mantisus

docs/04_upgrading/upgrading_to_v2.md

@@ -3,16 +3,41 @@ id: upgrading-to-v2
 title: Upgrading to v2
 ---
 
-This page summarizes the breaking changes between Apify Python API client v1.x and v2.0.
+This page summarizes the breaking changes between Apify Python API Client v1.x and v2.0.
 
 ## Python version support
 
-<!-- TODO -->
+Support for Python 3.9 has been dropped. The Apify Python API Client v2.x now requires Python 3.10 or later. Make sure your environment is running a compatible version before upgrading.
 
-## Change underlying HTTP library
+## New underlying HTTP library
 
-In v2.0, the Apify Python API client switched from using `httpx` to [`impit`](https://github.com/apify/impit) as the underlying HTTP library.
+In v2.0, the Apify Python API client switched from using [`httpx`](https://www.python-httpx.org/) to [`impit`](https://github.com/apify/impit) as the underlying HTTP library. However, this change shouldn't have much impact on the end user.
 
-## Update signature of methods
+## API method changes
 
-<!-- TODO -->
+Several public methods have changed their signatures or behavior.
+
+### Removed parameters and attributes
+
+- The `parse_response` parameter has been removed from the `HTTPClient.call()` method. This was an internal parameter that added a private attribute to the `Response` object.
+- The private `_maybe_parsed_body` attribute has been removed from the `Response` object.
+
+### KeyValueStoreClient
+
+- The deprecated parameters `as_bytes` and `as_file` have been removed from `KeyValueStoreClient.get_record()`. Use the dedicated methods `get_record_as_bytes()` and `stream_record()` instead.
+
+### DatasetClient
+
+- The `unwind` parameter no longer accepts a single string value. Use a list of strings instead: `unwind=['items']` rather than `unwind='items'`.
+
+## Module reorganization
+
+Some modules have been restructured.
+
+### Constants
+
+- Deprecated constant re-exports from `consts.py` have been removed. Constants should now be imported from the [apify-shared-python](https://github.com/apify/apify-shared-python) package if needed.
+
+### Errors
+
+- Error classes are now accessible from the public `apify_client.errors` module. See the [API documentation](https://docs.apify.com/api/client/python/reference/class/ApifyApiError) for a complete list of available error classes.