On the Contributions Search (Administration > Contributions > Search), we have added the ability to mass move contributions to a specified donor and/or mass update the Fund.  These options are found by clicking on the down aritem beside the Filter button:

After clicking Update All , you will get a Bulk Update prompt where you may mass re-assign the donor (using Update People ID ) and/or mass update the Fund (through Update Fund ID ) tied to the filtered list of contributions. 

For more detailed instructions, please refer to our Contributions Search article.