You check the disk size usage of the system using "df -h" command.  
Here in this case it shows 100% usage,

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44.193.7.75 | 172.31.1.61 | t3.small | null                                                                                                                                            
[ centos@workstation ~ ]$ df -h                                                                                                                                                        
Filesystem      Size  Used Avail Use% Mounted on                                                                                                                                       
devtmpfs        863M     0  863M   0% /dev                                                                                                                                             
tmpfs           890M     0  890M   0% /dev/shm                                                                                                                                         
tmpfs           890M   17M  873M   2% /run                                                                                                                                             
tmpfs           890M     0  890M   0% /sys/fs/cgroup                                                                                                                                   
/dev/nvme0n1p1   10G   10G   91M 100% /                                                                                                                                                
tmpfs           178M     0  178M   0% /run/user/1000                                                                                                                                   
                        

Now lets increase space, Follow the steps.

Choose the instance which consumed the disk space.

Click "Stop instance" & wait until instance is stopped.

Choose the volume and refresh and see if the volume has been increased or not.

Ensure "25 GiB" changed volume is refreshed.

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44.211.232.23 | 172.31.1.61 | t3.small | null                                                                                                                                          
[ centos@workstation ~ ]$ df -h                                                                                                                                                        
Filesystem      Size  Used Avail Use% Mounted on                                                                                                                                       
devtmpfs        863M     0  863M   0% /dev                                                                                                                                             
tmpfs           890M     0  890M   0% /dev/shm                                                                                                                                         
tmpfs           890M   17M  873M   2% /run                                                                                                                                             
tmpfs           890M     0  890M   0% /sys/fs/cgroup                                                                                                                                   
/dev/nvme0n1p1   25G   11G   15G  41% /                                                                                                                                                
tmpfs           178M     0  178M   0% /run/user/1000                                                                                                                                   
                        

Increase EC2 Disk Size