Let's say you your data in A1:A100 and the formulas in B1:B100 then do the following:

Select B1, press F2 and put a ' in front of the equal sign and press Enter. Now take a copy of B1 and paste it to for example G1 (to keep a copy of the original formula). You can, if you prefer, put a ' also i H1 to avoid the text spill over to the right of G1.
Now select B1:B100, take a copy and paste it as values to A1:A100. Select B1:B100 and press Delete.