backmann is correct... We need to know what 'client' you are using...
Also, what -
type of internet connection do you have
and Operating System
Whether or not you are allowing yourself to be an Ultrapeer
and, where you are running your system... at a school or at home or an office...
It would also be best for you to say how many UpLoad Slots you have configured and how many Downloads you are attempting at the same time. Plus, how many Ultrapeers or 'hosts' are you set to connect with as your minimum and maximum, and whether or not you are sharing a large number of files... Not the total sizes of the files, but the volume of files...
Basic rule is that the less you try to do at one time, the more you will be able to do at one time !
The more info you give in the beginning, the faster you may receive replies that help you !