@M_V and @yoav thank you very much for your replies. Yes, I need a new mechanic - I only use these guys infrequently as I prefer to try and do as much work as I can on my bikes, to help me learn, but there are some jobs that are beyond me due to a lack of tools.
I'll buy an 11-28 cassette (Shimano CS-HG80) and try that first. If I find I need to make more changes, I'll look at removing the smallest ring and increasing the size of the largest, but for now I think the cassette swap is the best option, especially as I don't know how old this one is. Thank you both again!
@M_V and @yoav thank you very much for your replies. Yes, I need a new mechanic - I only use these guys infrequently as I prefer to try and do as much work as I can on my bikes, to help me learn, but there are some jobs that are beyond me due to a lack of tools.
I'll buy an 11-28 cassette (Shimano CS-HG80) and try that first. If I find I need to make more changes, I'll look at removing the smallest ring and increasing the size of the largest, but for now I think the cassette swap is the best option, especially as I don't know how old this one is. Thank you both again!