My disc image encrypted file cant take more files. How can I change it?

Simple answer...make a new, bigger encrypted disk image, copy the files from the old one, then delete the old one.

 

When you create a disk image in Disk Utility one of the option fields is for size.

 

Make the size of the image larger than you expect to use allowing for future expanded use
Under image format, make it a sparse image or sparse bundle
When you put files in it, it will only take up the size you use and will expand as you use it to the sparse size you set