To clear Magento cache you need to login to Magento backend, navigate to System > Cache Management screen and use Flush Cache button to flush caches:
Javascript/CSS caches and Images cache can be flushed at the same screen with Flush Catalog Images Cache and Flush Javascript/CSS Cache buttons at bottom left.
Clearing cache when Magento admin backend is down
If you have no access to Magento admin backend due to some issue, the caches can be cleaned from the console, simply login to your Magento installation via SSH or FTP and delete all subdirectories under var/cache directory.
SSH users can use the following command to flush Magento caches:
$ find ./var/cache -type f -delete
FTP users can use the following command to cleanup Magento caches:
> mrm -r ./var/cache ; mkdir ./var/cache
Magenting accounts can clean Magento cache from the Store settings page with a single button click:
