Sometimes, memory of Android phone get filled up with photos, videos, offline maps or other media and "not enough storage space" warning is displayed to user. In this case, if user browses the Gallery application to delete some photos and videos, error message is prompted that "Not enough space. Delete unnecessary items such as ... pictures, videos...". It is not easy free up space in this situation, but following workarounds can be applied to resolve the issue.
Native or pre-installed file manager can be used to access the media. So, to remove some heavy photos or videos, user can start the file manager and look into the usual locations of media. Most photo applications save their images below /sdcard/DCIM and following to DCIM folder, and also check Pictures, Photos, Video, media, Music, and Documents for media. The camera files are mostly stored at /sdcard/DCIM/Camera on a phone whose camera option for storage has not been modified. Otherwise, the camera settings will still lead user to the storage location. If device does not have pre-installed file manager, then it can be installed from play store.
Other way is to uninstall some applications that are large in size. The internal storage can be made sufficient to launch the gallery application without insufficient memory error.
An alternative method is to connect smartphone to computer via USB then delete all unwanted photos and media from the Gallery. PC or laptop connected to mobile device will display media files stored in the memory.
Try to stop running applications which are not currently in use from Settings -> Apps. Clear data and cache of large applications which consistently store data in the phone memory. Apps like Whatsapp, Facebook, Skype and other chat applications often have large cache and data associated with them.