Retirement accounts including your IRA, your 401(k), your defined pension plans, your 403(b) if you work for a non-profit, 457 saving plans, any of these retirement accounts designate a beneficiary.
In some states, you can only designate as your primary beneficiary your spouse, unless you get your spouse's approval. You can designate a contingent beneficiary; however, which could be your trust. For these accounts, it's very important that you keep the beneficiary designations updated. The laws with respect to this vary from state to state.
There are often unintended consequences because someone has died, or someone has gotten married, or someone has gotten divorced and they fail to update the beneficiary designations.
In almost every case for a retirement account, you should be able to contact either the custodian, such as the brokerage house or the bank of the account, or your HR department and ask them for the proper forms to change the beneficiary designation. You have to read these forms very carefully. You can't just assume that you sign in one place. Each form is unique, each form requires you to read the small print. There again though, almost every single company has their own forms to do this.