Gryphon Carrera
 

Hello everyone!!! I'm a newbie to this forum/site so looking to tap into your collective knowledge.

I have a Gryphon Carrera (2005), yup!! It's been a very, very reliable bike for me..... I have travelled thousands of miles on it. As a consequence most of the rear mech is in a poor state of affairs - it's all the original. So, I have got my hands on a Shimano CS-HG300-9 cassette 12-36T (better for the hills around here). Can I use this as a replacement for the 11-31 that's knackered? Other comments/reviews on other sites say it's possible...!!? If so, which derailleur would you recommend to be compatible?
If it won't work....can you suggest a combo that would be a suitable replacement/upgrade? Crank is 34/48, (current) derailleur is Shimano Tiagra.
I don't want to spend too much as it was a cheap bike to begin with!!
Thanks in advance.

Done!! Figured it out myself.