Increase file upload size

I was about to upload my PDF files. Some of these files are larger than 10mb, but then an error message displayed in a pop up box saying:

An error occurred while trying to upload the file test.pdf

Invalid Security Token
-```

I've checked media configuration in Media > File Upload Limit and it seems like there's no configuration there on how to increase the file upload size.

Is there any way to increase the file upload size?

I've copied and pasted the php configuration file into my folder, increased the file upload size there and saved the changes. I've cleared cache and nothing has been changed.

Closing this thread as it's already fixed.