How can I negotiate lease terms, should I contact a lawyer?

The easiest thing to do is simply talk to your landlord. Most would rather renegotiate a slightly lower lease than completely lose a tenant.

Dear Kathy:
You can always try to renegotiate your lease. If you still have time on your lease, the landlord is under no obligation to renegotiate. You can also try and get the personal guarantee off the lease but I assume that would be difficult.
However, if you have been a good tenant then the landlord should want to keep you around. The first step is to simply make an appointment and state your case.
Remember a lease is supposed to be a legally binding contract so if you break it you can be liable for breach. If you are considering this then I would most certainly recommend that you seek legal advice.

You can negotiate yourself. Make sure you start off by stating positive points of you as a tenant (long term tenant, paid on time, no problems, etc). He must think that it is not a good business to let a tenant like you go. Remember,you must be Firm and Friendly.
Before you let the attorney review your contract make a list of items you want in the contract (terms,conditions etc) and give it to the attorney. Attorney fees, negotiate a flat fee and tell him/her what you want accomplished. Before you sign the contract, read it yourself. All the best.