Depends what sort of space error it is: if it's referring to internal storage, get a file manager from the Play Store (I use a free one called File Manager) and delete files you no longer need or move them to your SD card. Start with big files like videos, MP3s and photos.
If the issue is 'memory' (i.e. your phone splits internal storage between storage and an installation area):
- clear caches on all your apps
- remove apps you no longer use
- remove updates and data for apps you no longer use but can't remove
Failing that, you may be able to root the phone and reconfigure the internal storage - see the rooting sub-forum for your phone for more details.
