Cisco QOS for VOIP to specific sunet

Hi we have a VPN with one central location and about 130 smaller sites.
The central location is connected with 100/100Mbit

We have one location with subnet 10.3.30.x /24 and 20/1 ADSL connection (max speed for that site).
They have a lot of devices and many times the download or upload speed is all used and VOIP quality suffers (Cisco CUCM environment)

Both sides have Cisco routers.
Do i have to configure QOS on the central location router if I want to guarantee that VOIP packets have priority to that specific subnet? I have to change the router on that site for the upstream VOIP traffic I guess.

Config on central router now only contains this:

policy-map shape-to-100

class class-default

shape average 100000000 400000

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What should I add to give priority for VOIP packets to 10.3.30.x ?

Cisco Router on site (881VA) does not have any policy-maps, what is the most simple config to always guarantee 256Kbps to VOIP traffic? The VOIP servers are located in 10.1.154.x /24 network.

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