Update Delta uniform documentation to include ALTER enabling - 3.3 (#…

…3963)

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## Description

Update Delta uniform documentation to include ALTER enabling

docs/source/delta-uniform.md

@@ -61,13 +61,25 @@ CREATE TABLE T(c1 INT) USING DELTA TBLPROPERTIES(
   'delta.universalFormat.enabledFormats' = 'iceberg');
 ```
 
-You can enable UniForm Iceberg on an existing table using the following syntax:
+In Delta 3.3 and above, you can enable or upgrade UniForm Iceberg on an existing table using the following syntax:
 
+```sql
+ALTER TABLE table_name SET TBLPROPERTIES(
+  'delta.enableIcebergCompatV2' = 'true',
+  'delta.universalFormat.enabledFormats' = 'iceberg');
+```
+
+You can also use REORG to enable UniForm Iceberg and rewrite underlying data files, as in the following example:
 
 ```sql
 REORG TABLE table_name APPLY (UPGRADE UNIFORM(ICEBERG_COMPAT_VERSION=2));
 ```
 
+Use REORG if any of following are true:
+* Your table has deletion vectors enabled.
+* You previously enabled the IcebergCompatV1 version of UniForm Iceberg.
+* You need to read from Iceberg engines that don't support Hive-style Parquet files, such as Athena or Redshift.
+
 You can enable UniForm Hudi on an existing table using the following syntax:
 
 ```sql
@@ -156,4 +168,4 @@ The following <Delta> features work for Delta clients when UniForm is enabled, b
 - Delta Sharing
 
 .. <Delta> replace:: Delta Lake
-.. <AS> replace:: Apache Spark
+.. <AS> replace:: Apache Spark