Install the package by clicking the package link provided by Kaptio Travel.
The link will look like this: https://login.salesforce.com/packaging/installPackage.apexp?p0=04t06000000HQhC
For installing the package in sandboxes please change the url to point to test.salesforce.com, rather than login.salesforce.com.
It is recommended that when installing the package you choose the Install For Specific Profiles option and set all profiles to No Access.
You may need to acknowledge that you are installing a Non-Salesforce Application by checking the checkbox.
Last step is to click the blue Upgrade button. It may take up to 30 minutes to install the package.