How can I copy a downloaded file into lib/plymouth/themes ?

what is the outuput of:

lsb_release -a; uname -a

Thanks

This might be an access rights problem. Normal users are not allowed write access in system directories.
You most probably have to activate administrative rights (via sudo) to copy the file(s) there.

Not that I've done it - but my understanding is that changing the splash screen involves more than just copying a png file into the directory (as pointed out in a previous response by Manfred sudo will need to be used from a command line).

The procedure may vary based on what version of Ubuntu you have installed - hence the earlier request for more info by actionparsnip.

Instructions for Ubuntu 13.04 can be found here: http://ubuntuhandbook.org/index.php/2013/07/install-change-boot-screen-theme-ubuntu-13-04/

This link mentions both a gui tool and also gives a manual method using update-alternatives and update-initramfs. It also mentions problems with 14.04 but does provide links to possible fixes for this issue.

Just a word of warning - I tried the update-alternatives, update-initramfs method to test changing the configuration of plymouth n 14.04 and now have no splash screen. I did get back a scaled version of it momentarily, but in an effort to get it back to unscaled I wound up without it again. I may work on getting it back some more but it's not a big deal for me so...

Wish I had tried just replacing /lib/plymouth/ubuntu-logo.png (backing it up before hand of course in case that caused problems. Point is be careful.

Here is the output actionparsnip requested:
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.2 LTS
Release: 14.04
Codename: trusty
Linux stevens-laptop 3.13.0-48-generic #80-Ubuntu SMP Thu Mar 12 11:16:18 UTC 2015 i686 i686 i686 GNU/Linux
steven@stevens-laptop:~$

Thanks actionparsnip, that solved my question.