Hi Mohammad,
If upgrading 515E from R to UR ( Unrestricted ) you need software license
upgrade part number ( PIX-515-SW-R-UR= )
If you will be using a pair of PIX 515E in a failover architecture
One PIX must have FO ( Failover ) license and the other PIX 515E UR Lisence, refer to link bellow on software features license types for your 515E models.
Licensing Software features
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_data_sheet09186a00800b0d85.html
Licensing and Activation Keys
http://www.cisco.com/en/US/docs/security/pix/license/license.html
Other information : I suggest go over this link to prepare you for upgrade and
be familiar with new code 7.x specially comming from 6.x
UPgrading PIX 6.x to 7.X code, depricated commands and other changes
http://www.cisco.com/en/US/docs/security/asa/asa70/pix_upgrade/upgrade/guide/pixupgrd.html
When appliying license upgrade at the 6.x code once you upgrade to 7.x the existing license from
6.x is preserved, refer to license section on same link above.
Rate any helpful posts
HTH
Jorge
Jorge Rodriguez