hi Ger
Just use a small grinder with masonry disc and grind out or go an inch deep. Then hose down to get all the dust out before repointing.
Mix 5 sand to 1 cement which is a touch stronger than normal for repointing.
Can be messy without the right tools so go to bunnings and grab a very cheap trowel and a dutch joiner for about $20 to do the job.
Depending on the actual finish of the mortar as it may be flush,raked or round joined,you will need a brush,raker or round joiner also from bunnings.
3 or 4 hours later use water and brush to clean down the brickwork before it sets otherwise you will need some brick cleaning acid days later.
1/4 metre of brick sand and 1 bag of cement will be plenty.
Dont use that pre-mix crap.
Good luck.