have new computer want to install CS5 and deactivate from old. but need an older verison as cs5 is an update

you don't need the previous version that was upgraded.  you just need the serial number of the previous version.

but, if you want the previous version:

Downloads available:

• Suites and Programs:  CC 2014 | CC | CS6 | CS5.5 | CS5 | CS4 | CS3
• Acrobat:  XI, X | 9,8 | 9 standard
• Premiere Elements:  12 | 11, 10 | 9, 8, 7
• Photoshop Elements:  12 | 11, 10 | 9,8,7
• Lightroom:  5.5 (win), 5.5 (mac) | 5 | 4 | 3
• Captivate:  8 | 7 | 6 | 5
• Contribute:  CS5 | CS4, CS3

Download and installation help for Adobe links

Download and installation help for Prodesigntools links are listed on most linked pages.  They are critical; especially steps 1, 2 and 3.  If you click a link that does not have those steps listed, open a second window using the Lightroom 3 link to see those 'Important Instructions'.