In order to delete the old kernels run the following command
package-cleanup --oldkernels --count=2

this command will keep only 2 latest versions in your system

you can easy rollback the chnages from your last package update by the following steps

1. get the updates history:

yum history

2. look it closer (pick the update ID):

yum history info 37

3. rollback it:

yum history undo 37

to deny connection by user agent put the following line on your nginx config:

if ($http_user_agent ~ (Synapse) ) {
return 403;
}

For multi block:

if ($http_user_agent ~ ("Synapse|some_agent|and_another_agent") ) {
return 403;
}

in case with Engintron, put it to /etc/nginx/custom_rules

cp /etc/ips /etc/ips.bak

Add the ip to the file: /etc/ips
IP_to_ADD:NETMASK:IP_to_ADD_GW

Add the ip in: /etc/ipaddrpool
IP_to_ADD

Restart the service:
/etc/init.d/ipaliases restart

1) Run xfce4-appearance-settings, go to Settings and activate Enable
editable accelerators
2) In XFCE Terminal with the mouse select the in Help the Contents that
also says F1 at the end
3) To delete the option, press ‘Delete’ or ‘Backspace’. Backspace edits
the F1 to Backspace, so it re-assigns another key.
If you want e.g. F3 as the ‘Help’ button (like old times) you press F3