From New Refworks, select all the citations you would like transfer, then click share from the menu and select Export References, pictured below.
On the Export page, make sure you select "All References" under From and RIS Format under Format, then click Export. Your exported file should be downloaded automatically with the file name "export.ris" in your computer's Downloads directory.
Once the download has been completed, login into your Legacy Refworks account and click Refences and select Import.
When the Import page opens, do the following: