I am using CANVA software which only allows files up to 25 mb and my png's are over 30. I don't want to compress all the way down to JPG. I'd like to keep as much detail as possible.
Some thoughts. I have no idea what that software does.
There are some hundreds of different compression methods for PNG, but normally they do not compress a file much better than the other. The applications try to simply use a good compression variant.
But something (The big file size) is telling me you are using PNG for the wrong reasons. A PNG is recommended for graphics, logos or flat designs. If your composition has a photo (Which uses much space using PNG) think of using JPG with little to no compression.
The only case you need PNG is to preserve some transparency.
Some Online programs that claim to compress your PNG, actually make a JPG compression on Photos and then save them to PNG again.
Others simply reduce a 24-bit image to 8 bit.
If you have this case, try simply re-saving the file with Gimp.
You can also take a look at similar questions. Need png optimisation/compression advice
If you're not to bothered by external services or tools take a look at https://tinypng.com
It's a great service which can also batch convert (multiple files at the same time).