How can I fix my Triton Topaz T80i Hot water and pressure?

I have Triton Topaz t80i. Although it's working but, the water doesn't get hot. I still get a slight warmish water but the water pressure is really low. Is there a way to fix it ? If so please help. If not, then which would be the shower that can fitted in it's place without having to change the tiles etc.

B S Ahira
January 2011