"sharing a wireless connection at my work place", "How do i increase my browsing and downloading speed all to my self". Okay these are key statements to consider that then you would be doing the samething to your boss, the CEO, payroll, etc. where they couldn't "read or download file attachements from my emails".
If your work productivity is impacted, your best solution is to advise your supervisor / boss of the situation, and talk to the IT help your company uses. It may be as simple as too many devices on a single wireless point and have to install multiple wireless points instead, to a serious problem of the boss is stingy on paying for real internet speed but you need to prove the impact to business costs to get them to pay for more bandwidth.