Browse (or 'cd' on Linux) to the CELOXIS-INST-FOLDER. This is the folder in which you have installed Celoxis. For example, if your psa_11.1.0 folder is in C:\Celoxis, then go to this folder.
If you have installed Celoxis as a Windows Service then remove the service
Rename psa_11.1.0 folder to psa_11.1.0.old
Download the new psa_11.1.0.zip and copy it to CELOXIS-INST-FOLDER
Unzip
Now you should have two folders psa_11.1.0 and psa_11.1.0.old in CELOXIS-INST-FOLDER
Copy the files: db.properties, site.properties & license.properties from psa_11.1.0.old/webapps/psa/WEB-INF/conf to psa_11.1.0/webapps/psa/WEB-INF/conf