There are some web sites for testing the speed of your connection. You can google for them. However, you should probably start by asking your ISP. You bandwidth is determined by the type of service you have purchased from your provider.
Lastly, remember that bandwidth is often described in terms of kilobits per second (kbps). In aMule's preferences, you should enter values in kilobytes per second (kBps). To translate from kbps to kBps, you divide by 8.