You need to 'revise/ setup' your router settings again. Also, there could possibly be other factors such as:
a) Weather conditions,
b) ISP (Internet Service Provider) technical issues/ ugrades,
c) Outside interferences, etc.
*Edit: Added user's ID
That setting is a 'default' one. Visually, have you noticed any kind of improvement *(with the default setting)? If so, you can raise the setting in increments of 5MB (if you want but do not max. the speed - if you do, there'll be more frustrations onhand).
*Edit: Fixed grammatical and syntax errors.