SLS 3D printer to DMLS 3D printer I know that the SLS 3D printer stands for selective laser sintering,where as DMLS stands for direct metal laser sintering.

I want to know that,can i convert SLS 3D printer to DMLS.

By just changing powder(or another way?)
By just changing powder: No.
Changing the powder, the laser and the chamber, maybe you can get something, but it's not recommended.
DMLS machines use a sealed chamber with a flow of Argon, Nitrogen, or other gas to prevent oxidation of metal powder (and avoid fire or explosions).
Laser power for metal needs to be of higher power than that used por polymer laser sintering (SLS, SLM, LS, etc).
BTW. DMLS also need a metallic build plate to dissipate heat.