Hi Milan,
Have you looked at this doc? Perhaps it will help get you started;
Updating or Replacing a Cisco Secure ACS Certificate
Use this procedure to update or replace an existing CiscoSecure ACS certificate that is out-of-date or out-of-order.
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Caution This procedure eliminates your existing CiscoSecure ACS certificate and erases your Certificate Trust List configuration.
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To install a new ACS certificate, follow these steps:
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Step1 In the navigation bar, click System Configuration .
Step2 Click ACS Certificate Setup .
CiscoSecure ACS displays the Installed Certificate Information table on the ACS Certificate Setup page.
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Note If your CiscoSecure ACS has not already been enrolled with a certificate, you do not see the Installed Certificate Information table. Rather, you see the Install new certificate table. If this is the case, you can proceed to Step5.
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Step3 Click Enroll New Certificate .
A confirmation dialog box appears.
Step4 To confirm that you intend to enroll a new certificate, click OK .
The existing CiscoSecure ACS certificate is removed and your Certificate Trust List configuration is erased.
Step5 You can now install the replacement certificate in the same manner as an original certificate
From this doc;
http://www.cisco.com/en/US/products/sw/secursw/ps5338/products_user_guide_chapter09186a0080204de1.html#wp180743
Hope this helps!
Rob
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