How to update the table with information of the update command written in table

example
Table name mstupdates, which contains the fields table, field,old,new
table      field      old      new
mstchvs      aa      1      19
transbcc1       bb      32      343

table refers to table to be updated
field refers to column name
old refers to old value
new refers to new value
of the table.

How to use update command.

update table set field=nv where ov=ov