It's possible to transfer content from one WordPress install to another. Posts, pages, comments, custom fields, categories, and tags are all included and should work without too much additional effort. Media, pictures, and other data may not work without manual intervention.
This process has two steps: exporting your old content into a file, and uploading this file to your new site.
Step 1: Exporting Content from Old Site
The first step is to export your old WordPress site into the WordPress export file format. To do this, you will want to navigate to "Tools" and then "Export" on your old site. It should generate a file that you can save to your desktop.
Step 2: Importing Content into New Site
Now that your content is stored in a file, you can upload it to the new site. Log into your Dashboard and then click on "Tools" and then "Import." Choose "WordPress" and then import your file. It may take a few moments to upload and complete: so be patient! Once complete, take a look at your site and fix any issues that may have occurred.