Some forms in HR (and possibly other modules) and configurable, however if you are looking to change the ordering of items and the width of fields etc then you are going to have to customise the form, so you will need somebody who at least knows the basics of Oracle Forms development.
Is there any document available for the same?
Should i have to customise it through form developer using .fmb file?
Not really any documentation specific to this, however you should consult the Oracle Applications developer guide. The "correct" way to make such a customisation is to copy the module and "XX" it so that it becomes custom. Then make your changes on top of that and redeploy as a new module, with new form/function setup. If that is not possible then you should register the module as being impacted so that it is flagged up should a patch affect it in the future.