I have an all on four denture on the lower jaw. Can it easily be changed to a snap in denture? What would be involved?

Actually, it is easy. I do this often & vice versa. First find out if your implants were placed on angles (despite having bone, some doctors don't put them in straight; not a fan since I place them in straight). Second, find out if the implant brand can have Zest attachments placed into them.  You will then need a new set of teeth.  I have several examples.  Good luck justbeckyg

It depends on the placement and position of the implants. The abutments which connect the implants to the bridge would have to be changed. Also, the bridge would likely have to be converted to an overdenture. The All-on-Four bridge is the most ideal option.