Is there any way to export data to CSV file and then import updated data? I have a website I started to build couple years ago. But the website itself grew up to something bigger, with more fields and details - and old data are missing these. E.g., recently added Long./Lat. fields but old content doesn’t have them. So I wonder if it’s possible (and what module) to export all data into csv file, update it (I think it's much easier than open one by one node) and than import the updated data? Or something like that.

Thanks for any help.
If you want to do it that way, use Views data export. Here is an excerpt about it from the module's project page:

... designed to provide a way to export large amounts of data from views. It provides a display plugin that can rendered progressively in a batch. Style plugins are included that support exporting in the following types:

CSV.
Microsoft XLS.
Microsoft DOC.
Basic TXT.
XML.


Then, re-import using the Feeds module. Here is an excerpt about it from the module's project page:

Import or aggregate data as nodes, users, taxonomy terms or simple database records.

One-off imports and periodic aggregation of content
Import or aggregate RSS/Atom feeds
Import or aggregate CSV files
Import or aggregate OPML files
PubSubHubbub support
Create nodes, users, taxonomy terms or simple database records from import
Extensible to import any other kind of content
Granular mapping of input elements to Drupal content elements
Exportable configurations
Batched import for large files