If your Coppermine gallery tell you that you cannot upload files larger than xxMB, you should check your Coppermine settings. You can change this by following these steps:

Log in to your Coppermine gallery as Administrator --> Click 'Config' --> Expand the menu for 'Files and thumbnails settings' --> At the 'Max size for uploaded files (KB)' field type how much is the maximum size of picture to upload. Notice that the size is in KB. 1MB=1024KB --> When done setting, click the 'Save new configuration' button at the bottom.