first of all when i brake there is a click and on bumpy surfaces a rattle. i took the wheel off and the sliding caliper seems wobbly and loose into the main brake part and wont tighten

secondly is there any form of upgrade or replacement brakes?

Sounds like the slider pins have dried out and have worn, you may need new calliper brackets and pins. I doubt the calliper brackets are available, so look for good scrap ones.

The callipers don't really need secured, the force is taken up by the calliper brackets (carrier) directly from the pads on the disk, so perhaps the pads are a loose fit in the brackets due to rust or poorly fitting pads. The calliper just squeezes. Check it against the other side.

Generally you should not need an upgrade, replace worn parts, get good quality parts and replace the fluid regularly.