Use the fix_vel option in uvmat to remove vectors with low correlation (red vectors), and black vectors. Before running fix_vel, adjust the correlation threshold in view_field, so that red vectors are mostly erratic. A threshold about 0.3 is generally appropriate. In fix_vel, you should keep the vectors vec_F=2 (Hart) which are not precise but provide a valuable preliminary estimate for CIV2.
To check the result, you should come back to view_field. The removed vectors appear in magenta, or they are not seen if the option see_false (upper right) is off.
Note that this 'removal' operation is reversible: it modifies a flag (FixFlag gets a 1 as the second digit, e.g. FixFlag=10 in the absence of other rejection criteria) but all the vectors are kept in the files. So you can run again fix_vel with different criteria (for instance different thresholds on correlations).
Hand removal is also possible (but not advised for a long sequence of fields!). Get the mouse cursor with the pushbutton select and left click to select vectors. Click the pushbutton record to record the changes. Such removal is then recorded in the netcdf file by setting to 1 the second digit of the flag vec_F. Therefore it is not erased by automatic fix programmes (which act on FixFlag). Inversely, if you manually select a flaged (removed) vector, and push record, you rehabilitate it (you set FixFlag=0).