Altium impedance setting for differential ,and single ended high speed paths

Example application

HDMI pcb path impedance

• Each HDMI channel is comprised of 4 TMDS pairs. Each HDMI channel set shall be routed primarily on the top or bottom layer as a group or alternately routed as a group on internal layers. Each TMDS signal shall have a single-ended impedance of 50 Ω ± 10%. Each TMDS pair shall have a differential impedance of 100 Ω ± 5%. 
• Read more.

Schematic - Set differential pairs in schematic for required nets

• Use differential pair tool

• Set label 100Ohm

• Place them on nets 

Impedance matching/ set impedance to PCB group of paths

• use the blanket tool in schematic design group signals with the same impedance 30Ohm / 50Ohm

• Use parameter set

• Rename Parameter set to 50Ohm

• Use the blanket tool 

• Draw a square using a blanket tool around the pins that you need to be 50Ohms

• Place 50Ohm Parameter set to blanket

PCB Editor 

• Calculate PCB pathwidth according to required impedance (50Ohm/ 80Ohm/ 100Ohm)
• Set new rules each nets in Design Rules
• Set impedance