Extensions will be granted only for extraordinary events that are beyond your control, such as illness. You cannot get an extension simply because you have other assignments due at the same time.
For all extensions, you must get prior approval from the lecturer (where the delay can be foreseen). To be considered for an extension, approach the lecturer concerned as soon as possible, bringing any documentary evidence that supports your claim. The lecturer may grant an extension, may vary the specification of your assignment, or (in truly exceptional cases), may vary your assessment in some other appropriate way.
Extensions on medical grounds require a medical certificate (no exceptions!).