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:
If Magento admin interface is inaccessible
If you have no access to Magento admin interface 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 of 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