After reaching an investigation entity (such as investigation, study, assay, source, protocol, sample, or data file), you can download that entity, in whole or in part. When deciding how much to download, keep in mind the following points:

http://isatab.sourceforge.net/docs/ISA-TAB_release-candidate-1_v1.0_24nov08.pdf

Each download option has a button on the Investigation Details page.

Download Full Data (602.82.48 GB zip) Download Selected Metadata  Add to Download

The following page family describes the various methods of downloading data.