Many android devices , especially Android Cell Phones (HTC Wildfire, HTC Wilfire S, Samsung Galaxy Ace, HTC Salsa, HTC Desire) have the problem of Low Internal Memory or Internal Memory Full. Most of these devices has the internal memory from 180 MB to 512 MB. When you purchase a new device out of the available memory around 40 MB is already eaten by the Andoroid OS, Application related services, Applications which comes pre-installed with your device. It is not that Android OS takes lot of space, but the apps and the related data takes more space.

There are few easy and efficient ways to clear up the internal memory.
Go to Settings->Manage Applications and follow the below steps

1. Move the Applications to SD Card

Check for the applications which are downloaded by you. E.g. Skype, Angry Birds or any other games or apps one by one. In application details if you see the button "Move to SD Card" then you can click on it to move it to SD Card. The application will be moved to SD Card and considerable space will be freed up on your internal memory. In my device I freed up around 15 MB on my internal memory by moving Skype to SD Card. Like wise you can move applications one by one to the SD Card.

If the button reads "Move to Phone", it means the application is already installed on SD Card.