You can download Designer Pro+ from here.
Double click on the .exe file to start the setup:
Simply follow the instructions onscreen and click next to proceed. It is recommend to close any other open applications to prevent possible errors from happening
In order to continue with the installation, you will need to agree to the terms of the license agreement. Click here to view the EULA.
Next, enter your name and company (optional).
If you wish to change the location where Xara is installed, you can do so here.
If you are happy with all the settings, click next to install. Xara will not proceed to install Designer Pro+ onto your computer.
Afterwards, Xara will start and ask to connect to Xara Cloud to authenticate.
Please see this article on activating Xara Designer Pro+.