John is right... you can edit multiple jobs in one go, but there is no quick way to select the jobs with a particular frequency. I need to look at more sophisticated ways of filtering the job list, not just for frequency, but really any field, e.g. jobs above/below a certain price, all one off jobs, all jobs only done on a Monday, etc.
In the meantime Tony, if you want me to change your 4 weekly jobs to monthly and your 8 weeklys to 2 monthly, I'm happy to do that for you.
You could also consider moving to 5 and 10 weekly, if you want to keep your jobs to stay organised into their specific days/weeks.
Another option would be to stick with 4/8 weekly, but rearrange your work so that there are a couple of days spare.
Finally worth mentioning, if you want to take a holiday, it's possible to shift all your work forwards in one go.