A few simple habits keep your box fast and trouble-free. Each one has a help video on the How-To page if you'd rather watch than read.
Settings (gear) → Storage → Cached Data → OK. Afterwards some apps may say they're opening for the first time. That's normal.
Open File Manager (yellow folder) and empty the contents of the Download folder and any movie-app folders (e.g. Bee TV). Use multi-select → Select all → Delete, then check your storage again.
A reboot closes anything running in the background and frees up RAM. Do it at the end of maintenance, or any time the box feels sluggish.
Apps crashing back to the home screen, a 'bubbles' background with missing shortcuts, downloads that won't finish, or jittery menus. Run maintenance to clear it up. (Buffering is usually a separate, network issue.)
Never reset the unit, erase Nand Flash / internal memory, or clear folders you don't recognise. You could need a full reprogram. See the Cautions page.