HELP WITH RESIZING UNWANTED PARTITIONS ON EXTERNAL DRIVE

Hi; does anyone know of a safe way to resize partitions that are no longer used on a Mac with El Capitan? I have an external drive which has 3 partitions and I want to reclaim space from one of them. Unfortunately, disc utility is causing me great difficulty as I can delete the partition but have trouble resizing. I don't want to make a mistake and lose data. How can I resize safely with disc utility? The pie chart is not usable with voiceover. Alternatively, does anyone know of a good partition manager that can be safely used with voiceover? Thanks.