At Umbler you can unzip files with the .ZIP extension directly through the Control Panel, going to Website > Files > Manager:

Hovering the file with your mouse should reveal the unzip option:

The files will be unzipped directly into the containing folder, and the folder structure of the zipped file will be maintained. This process may take some minutes, it all depends on the size of the file and the compression ratio.

Other extensions

Extensions like tar, tar.gz & tar.bz2 can be unzipped using SSH with the following commands:

#tar: 
tar -xvf file.tar 

#tar.gz: 
tar -vzxf file.tar.gz 

#tar.bz2: 
tar -jxvf file.tar.bz2