Update alter (#1921)

* Update alter

* Update docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md

* Update docs-2.0/3.ngql-guide/11.edge-type-statements/3.alter-edge.md

* Update 3.alter-edge.md

* Update docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md

* Update docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md

---------

Co-authored-by: cooper-lzy <78672629+cooper-lzy@users.noreply.github.com>
Co-authored-by: abby.huang <78209557+abby-cyber@users.noreply.github.com>

docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md

@@ -10,6 +10,11 @@
 
 - The property name must be unique in a tag. If you add a property with the same name as an existing property or a dropped property, the operation fails.
 
+- Only the length of a `FIXED_STRING` or an `INT` can be increased.
+
+- Only the data type conversions from FIXED_STRING to STRING and from FLOAT to DOUBLE are allowed.
+
+
 ## Syntax
 
 ```ngql
@@ -41,6 +46,9 @@ nebula> ALTER TAG t1 ADD (p3 int, p4 string);
 nebula> ALTER TAG t1 TTL_DURATION = 2, TTL_COL = "p2";
 nebula> ALTER TAG t1 COMMENT = 'test1';
 nebula> ALTER TAG t1 ADD (p5 double NOT NULL DEFAULT 0.4 COMMENT 'p5') COMMENT='test2';
+// Change the `p3` property to INT8 
+nebula> ALTER TAG t1 CHANGE (p3 int8, p4 string);
+[ERROR(-1005)]: Unsupported!
 ```
 
 ## Implementation of the operation

docs-2.0/3.ngql-guide/11.edge-type-statements/3.alter-edge.md

@@ -10,6 +10,10 @@
 
 - The property name must be unique in an edge type. If you add a property with the same name as an existing property or a dropped property, the operation fails.
 
+- Only the length of a `FIXED_STRING` or an `INT` can be increased.
+
+- Only the data type conversions from FIXED_STRING to STRING and from FLOAT to DOUBLE are allowed.
+
 ## Syntax
 
 ```ngql