The other answers here are generally discussing the mechanics of the answer . . . which is fine. In brief, all agents should be kept informed, and you can do it so long as you haven't signed an exclusive agreement. (If you have, you need to get released from that agreement first.)
The bigger question, though, is choosing an agent that'll best meet your needs. That means a familiarity with the geographical area, a familiarity with the type of property you're looking for, and a compatability with each other--buyer and agent.
Sometimes it makes sense to use 2 agents at the same time. Perhaps you're looking in 2 different states, and one or both of the agents is only licensed in one of the states. Sometimes you might be looking at 2 wildly different types of properties. Those situations exist, but they're relatively rare. And it doesn't sound as if they apply in your case.
You haven't explained why you're dissatisfied with your current agent. Think it through. If there are legitimate reasons (the agent doesn't know the geographic area you're interested in, the agent doesn't promptly follow up on your calls or e-mails, etc.), then certainly consider terminating your relationship with the first one and finding another one. But if it's just because you've ended up in a multiple-bid situation, that happens to all agents.
Whatever you do, though, be absolutely honest and transparent with all agents involved.