If you have statements for the accounts, try calling the company who is sending them to you and requesting access. If you need more assistance than that, try finding a local fee-only advisor (like myself) who can give you a hand.
You might also call the HR departments at both companies. They should be able to steer you to the plan providers and help you access your funds. Once you have located your accounts, then you must decide what to do with the funds in your retirement plans. In most cases, it's best to roll them to an IRA. That will generally give you more investment options and save you money in plan fees. That said, there are times when it makes sense to keep you money in a qualified retirement, not an IRA. That's usually if you have concerns about being sued, for any reasons. Qualified plans provide greater creditor protection than IRAs. You want to consider talking with a financial advisor before making a decision. Hope this helps.
Most retirement plans like this have an outside custodian such as Fidelity, Vanguard or similar companies. As Daniel suggested, usually the contact information will be on your quarterly statements from the plan. That's who you want to call. If you don't have statements then as Rich advised, call the company you worked for directly and they can tell you who the custodian is and how to reach them. Once you reach the custodian and convince them you are the owner of the account they should be able to explain what you have and help you make any changes you may wish to make.
Now once you have the contact info and some basics on the two accounts, you need to decide what it is you're trying to accomplish. This gets complex because your best options will depend of things like your current age, current employment & health situation, other financial holdings, things like that. Are you wanting to make a withdrawal? Are you wanting to consolidate the two accounts into a new IRA? Are you wanting to rollover these two accounts into a new active plan at your current employer? All of these questions will lead to different counsel. So, as you decide what you wish to accomplish you do need to consider getting a qualified person to give you some advice in my opinion. Once an egg is broken there is no going back! :)