I have caps on my front teeth. They are separating and becoming bucked foward. Can caps be replaced to fix this problem? (Photo)

Without seeing X-rays and only these photos, I would bet you will need these teeth extracted and need to look into dental implants.  I would schedule a consult with a board certified periodontist and experienced cosmetic dentist.  Tough case, but will look great in the end.   Good luck.  

Hi:You can replace the existing caps with new caps, however, it might be best to find out why the teeth have moved.Best,Dr. Maddahi

You need to figure out why your teeth are shifting first before considering any new dental treatment. I would not recommend replacing the crowns on the front teeth because they will be very wide and bulky to close that much space. If you have bone loss causing the issue, the teeth may need to be removed. If you have excessive force on the teeth moving them, that needs to be addressed and orthodontic treatment done to move the teeth back to their proper position. Teeth can separate and bulk forward from long term use of CPAP masks. If that's the case, you should try to switch to a cannula type mask or an oral sleep appliance to prevent further shifting of the teeth.