Visit the Solr wiki pages for more information:
https://wiki.apache.org/solr/UpdateXmlMessages
https://wiki.apache.org/solr/Atomic_Updates

Here's the structure of the update operation:

<add commitWithin="">
    <doc boost="">
        <field name="" boost="" update="set|add|inc">

Optional attributes for the "add" element:

• commitWithin: (milliseconds) time for the document to be committed.
  
  

Optional attributes for the "doc" element:

• boost: (default: 1.0) a float number for the document boost value.
  
  

Optional attributes for the "field" element:

• boost: (default: 1.0) a float number for the field boost value.
  
  
• update: "set" | "add" | "inc"
  
  With:
  
  • set: sets a value (if null remove the value, or, in the case of a multi-valued field, remove all the values).
    
    
  • add: adds a new value to a multi-valued field.
    
    
  • inc: increments a value by a specific number.
    
    
  Important:
  If none of the document "field" elements sets the "update" attribute, then the operation will be considered an "add" operation.
  Which means that the document will be added if it's a new document, or updated if it was already added (missing fields will be set to null or to a default value).
  

Make sure to add the fields "id", "field1", and "field2" to your SchemaXml.

<add>
    <doc>
        <field name="id">1</field>
        <field name="field1" update="set">field1 1-1</field>
        <field name="field1" update="set">field1 1-2</field>
        <field name="dynamicField1_s" update="set">dynamicField1_s 1-1</field>
    </doc>

    <doc>
        <field name="id">2</field>
        <field name="field2" update="set">field2 2-1</field>
        <field name="dynamicField2_s" update="set">dynamicField2_s 2-1</field>
    </doc>

    <doc>
        <field name="id">3</field>
        <field name="field1" update="add">field1 3-1</field>
        <field name="field1" update="add">field1 3-2</field>
        <field name="field2" update="set">field2 3-1</field>
    </doc>
</add>

Here's an example of http requests (using curl):

curl http://localhost:8983/solr/COLLECTION-NAME/update?commit=true \
-H "Content-Type: text/xml" \
--data-binary '<add><doc><field name="id">1</field><field name="data_s" update="set">beta</field></doc></add>'

Here's an example of an http request (you can copy paste it in your browser):

http://localhost:8983/solr/COLLECTION-NAME/update?update.contentType=text/xml&stream.body=<add><doc><field name="id">1</field><field name="data_s" update="set">beta</field></doc></add>

You can also force the commit by running one of the following URLs (you can copy paste it in your browser):

http://localhost:8983/solr/COLLECTION-NAME/update?commit=true

http://localhost:8983/solr/COLLECTION-NAME/update?stream.body=<commit/>