How do I change a field type from integer to decimal?
Ok, I found a good solution to solve my problem.

Modules required


Helper
Devel (this is not strictly necessary)


Steps


Enable Helper module;
Enable Devel module;
Enable the block Execute PHP;
Paste and execute this code in the block: FieldChangeHelper::changeType('field_myintegerfield', 'number_decimal');
Edit display format for node where the field is being used;
Edit Views where the field is being used to fix the format settings (If necessary);


If you don't want use Devel and can use Drush:


Enable Helper module;
create a new file in root Drupal folder, i.e. name it: intToField.php

&lt;?php
FieldChangeHelper::changeType('field_myintegerfield', 'number_decimal');
?&gt;
launch the drush command: drush src intToField.php
Delete the file;
Edit display format for node where the field is being used;
Edit Views where the field is being used to fix the format settings (If necessary);