change shipping fee

Hi, i am a new user to Zen cart, the website was built by someone who understood the programme but is away on holiday and we need to change a few things in the shipping

We currently have a flat rate under £30 and its £0.99p i want to up the rate to £1.25 anything over £30 is free, also we want to change the options of postage over £30 currently we have standard post for free but signed for is set at £0.99 plus £0.79 for signed delivery how do i change all the above ?

I hope you can understand the above and help

Many thanks in advance
Rcbits