Manage Apple Music Membership

Join on your Mac or PC

1. Open iTunes. Make sure that you have the latest version.
2. In the upper-left corner, click the Music  icon.
3. From the top of iTunes, click For You.
4. Click Start 3-Month Free Trial.
5. Select Individual or Family membership, then click Next.
6. If prompted, enter your Apple ID and password that you use with the iTunes Store. If you don't have an Apple ID, click Create Account.
7. You might be asked to validate your billing info. After you add a payment method, click Join. You can use store credit to pay for your Apple Music membership, but you must have enough store credit for your first renewal.
8. If prompted, agree to the terms and conditions.

More details wise.

Click to open iTunes and sign in to your Account Information, or use the steps below:

1. Open iTunes.
2. Click Sign In and enter your Apple ID.
3. Click your name, and select Account Info from the menu.
4. Enter your password again.
5. On the Account Information screen:
1. Scroll to the Settings section. 
2. To the right of Subscriptions, click Manage. If you have more than one subscription, then click Edit to the right of Your Membership (Apple Music Membership). 
3. To the right of Automatic Renewal, select Off. When asked to confirm, click Turn Off.
4. Click Done to return to Account Information, and then click Done to return to the iTunes Store.

On your iPhone, iPad, or iPod touch:

1. In Settings, tap Music.
2. Turn on Show Apple Music.
3. Tap Join Apple Music.
4. Tap the For You tab, and then tap Start 3-Month Free Trial. 

Visit: https://support.apple.com/en-us/HT204939