How do you get a clam to detach?

[12gallonbaby]

My clam is currently on a shell because i had no rock for him to attach to. now i have some new pieces of rock and he is getting too big for the shell so my question is how do i get him to let go without hurting his foot?

 

[sbreefer]

carefully cut with a razor and leave as much fiber as poss.
Do not pull it loose you can kill it.

 

[deansreef]

cut the foot???

 

[o.c.d.]

No cut the threads from the foot as close to the rock as possible. and try not to tug to much on the clam.