Please back up all data before making any changes.
To copy files from one local account (A) to another (B), log in as A and move or copy the files to the Public subfolder of the home folder. The home folder is represented by a house icon in the sidebar of a Finder window.
Now log in as B. Triple-click anywhere in the line below on this page to select it:
/Users
Right-click or control-click the line and select
Services ▹ Open
from the contextual menu.* A folder should open. Inside it are the home folders of all users. Open A's home folder, and inside it, the Public subfolder. Select and drag the files to wherever you want them. They should be copied, not moved.
If you get a warning about not having permission, log back in as A, select the Public folder, and open the Info dialog. The dialog should show that "everyone" has "Read only" access in the Sharing & Permissions section. If not, change the setting. You might first have to click the padlock icon in the lower right corner of the dialog and authenticate as an administrator.
Click Apply to enclosed items. Log back in as B and try the copy operation again.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select
Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You may not see what you pasted because a line break is included. Press return.