Lease terms vary from contract to contract, but if you can't fulfill your terms, you'll need to renegotiate with your landlord. If your location is in demand, they may let you out of the lease unconditionally,
or perhaps they'll allow you to find another tenant. If your landlord does agree to release you, make sure you get it in writing to protect yourself legally. If your landlord doesn't want to release you from your obligations, you'll be forced to sacrifice your security deposit, pay the remaining amount until the landlord can find another tenant, or both. Keep in mind that it doesn't take much time for an attorney to review a lease, so if you're considering skipping out all together, make sure you know what the repercussions will be.
For more on office leasing, be sure to read Important Commercial Lease Terms to Familiarize Yourself With.