Often with the Bigip-VEs, installing an image or hotfix via the GUI will be impossible because the volume drop-down menu is empty:

F5GUInoVolumes

First verify the name of the image that’s been uploaded.  It should be in /shared/images

(tmos)# bash
# ls -l /shared/images/*.iso
-rw-r--r--. 1 tomcat tomcat 2096115712 2020-03-11 09:56 /shared/images/BIGIP-13.1.1.4-0.0.4.iso

Then install the image via tmsh with the create-volume option:

# tmsh

(tmos)# install sys software image BIGIP-13.1.1.4-0.0.4.iso volume HD1.2 create-volume

(tmos)# show sys software status
----------------------------------------------------------------
Sys::Software Status
Volume Product Version Build Active Status
----------------------------------------------------------------
HD1.1    BIG-IP  13.1.0.8  0.0.1     yes               complete
HD1.2    BIG-IP  13.1.1.4  0.0.4      no  installing 10.000 pct

At this point you can go back to GUI, watch the installation complete, and boot to that volume.