You need to contact the plan administrator. If you are unsure of who this is, typically your HR contact should have that information for you. Once you contact your plan administrator, you want to let him/her know you are wanting to either roll your old 401K into a rollover IRA or take a distribution. Traditionally this involves filling out a form and sending it back the plan administrator. I highly recommend sitting down with your financial advisor to discuss your options and have the proper accounts opened if you elect to rollover this distribution. Just remember once you get the check, the clock it ticking before it becomes a taxable event!!
You need to contact the plan administrator for the plan and get a distribution form directly from them. From there, you have multiple options on how to distribute the funds. I recommend consulting your financial adviser prior to distributing the funds.
The first thing you will want to do is determine who the plan administrator is. This company should be the one to process your distribution. You can start by contacting HR from your former employer.
Once you have the plan administrators contact information you can get in touch with them to process your distribution. This is where it is important to make sure you know what your are doing and as a result I would highly recommend consulting a certified financial planner in your area.
Most plans will include an 800 number for the plan administrator right on the quarterly statement. Just call them up and tell them what you want to do. You can move the funds to your current employers 401k or into your own tax deferred IRA account with no tax penalty through what is known as a direct rollover. If you remove the money for cash, you will have to pay tax (and a penalty if you are under 59.5).
If you have a Financial Advisor, they can do a conference call with you and the institution where your account is held at. Depending on the firm, they may process request over phone, online or by form and a Financial Advisor can make sure everything is done correctly